Thanks for letting me know @meATroon.
A few follow-up questions:
Thank you for your patience here 
Hey @meATroon,
I’ve split your posts into its own topic in order for it to receive proper attention, and we believe your situation may be a bit different from the other thread.
The first thing we see, is that your device is indeed giving us OOM error messages in the system logs. After digging into this a bit more, we found that your Roon library is on the larger size - almost 350k tracks.
In order to make ARC work and to support operations with poor or limited connectivity, Roon needs to synchronize information about your music library onto your mobile device. While the data synchronized is much more compact than what is stored in the Roon Core, for this large of a library it is likely still too big for a mobile device.
All of this said, when you play music in your car, is your device also plugged into a charger of sorts? It could be the case that the phone is getting warm due to this as well. More than likely its the amount of energy it takes to process the size of your library.
Aside from limitations in device performance, there are also restrictions on resource usage imposed by Apple and Google which make this scale of data transfer, synchronization, and storage impractical within a mobile app.
With this, I don’t have a direct solution for you, at least not yet. We’re still investigating this. One thing to test, would be to separate your watched folders in your core settings into smaller buckets, and disable a few of thing to limit the library size. From there, go about your arc routine as usual, and see if your device still runs into the same issues.
I’ll be monitoring this thread for your reply
I assume the Out of Memory errors are coming from my phone and not my core, correct? That would make sense. The only thing that I wish would happen is that it would just become less performant (which would be very understandable). Instead it just freezes the UI completely and prevents any control over the media (the current song continues to play, but no new song begins once it ends). Given the multithreaded nature of iOS is there anything that can be done to at least allow it to respond to pause or skip, especially in a car driving situation?
The heating up only happens when the UI is frozen. When everything is responsive there is no excessive heat coming from the phone (and, for what its worth, the heat comes from the upper left part of the phone).
thanks so much for getting back to me about this
Hey @meATroon,
Yes you are correct in that we’re seeing the OOM errors on the mobile device and thank you for the additional info! We’re continuing to investigate this issue further. In the meantime, can you please update to the newest Roon and Roon arc builds, and let me know if your issue persists?
We don’t yet have a clear workaround quite yet, although if you’d like to test out setting up a smaller watched folder for a smaller subset of your library, that could produce different outcomes to the issue.
Outside of this, our team are actively looking into other possible solutions, and I will certainly keep you in the loop on any progress made 
I updated everything and it did not really improve. Then, I completely removed ARC (and its data) from my phone and reinstalled it. I let it do its syncing thing while still on my local network and now it has been working much more reliably. I hope I am not jinxing it, but that may have really made it usable away from home. I will keep stress testing it (you know, that hard work of listening to music) and I’ll report back if any issues pop up again.
Thanks for getting back to me along the way. Even while things aren’t working as I hope, roon always remains my favorite piece of software.
I hope it continues working for you. ARC has become largely unusable for me again.
Same here. Have been working since the last update but now it’s unusable again. Even freezes when browsing the settings
I installed the latest update, hoping it would fix some of these issues, but no dice. The phone gets so hot that I am concerned about compromising the display. I do have a large library, but I also have a very powerful phone with loads of free storage (iPhone 13 Pro with 256 GBs). I seriously looked at segmenting my library, but that would introduce a weird organizational logic to my collection and I would be compromising availability to those at home just so I can listen while I am at the office. I am willing to be patient with this, but so far it has been a failure.
I really feel like I was the perfect candidate for this functionality:
I almost exclusively listen to my large collection of local files. This means that I don’t place as much value in my tidal subscription (usable away from home since the beginning), which I mostly use for discovery
I have really fast, symmetrical fiber 1GB up and down. Fiber is most commonly using CGNAT which presented no problem for remote usage of my Synology NAS. So I had to pay an extra $10/month to my ISP just for roon ARC.
Both of those have proven to be impediments to success.
Hey @meATroon,
You have my apologies that we haven’t yet pinned down the culprit behind these Arc issues. We’re still spending a good amount of time investigating things. We do have confidence around the idea of Arc struggling to decode large amounts of higher res files, but things are still murky.
I will of course keep you in the loop as we continue to deep dive into this issue
Thanks for keeping me updated and I am happy to hear that this is something that might get fixed. One thought I was having that might be an issue if the database is stored locally on the phone: I have been entering my “Unidentified” albums into MusicBrainz and steadily changing (Re-identify Album) quite a few entries. Probably not an issue for a modern database but just thought that was slightly unusual usage.
Replying to keep this thread alive. I have an iPhone 13 Pro Max and experience all the above. I’ve replied on other threads as well just so I can follow along and get an answer eventually.
Just FYI, you can set any thread from tracking to watching, with the button at the bottom. Then you get a notification for every new post in the thread. Posting in the thread is not necessary.
Hi All,
Following up on this thread, we’ve made some crucial improvements to Arc on the latest release. Please update to the latest build and let me know if you continue to experience this issue
Hi @benjamin ,
Thank you for the update. For my situation, unfortunately, it made it worse. It immediately freezes as soon as I play a track.
My situation is also worse. I get a poor connection message regardless of whether I am on wifi or cellular. It is completely unusable. I will let things settle down in case the core is doing something due to the update and I’ll uninstall and reinstall ARC on my phone and try again.
I’m confused. Does it freeze or heat the iPhone 
Thanks for this information. I have not seen this improvement in the release notes …
However I will test it.
no progress 
Roon ARC 1.0 (128) on iOS still freezes, crashes and heat up the iPhone. Tested with WiFi and without playing any song.
I wish the Roon team would fix the existing bugs before adding new functionalty (e.g. Car Play)