Indeed. My solution has always been to not buy the latest model, particularly when it comes to anything Android!
I’m not hugely into mobile devices so I’m quite happy with my Samsung A20e. Connects every time to Roon and does everything that I need it to do. There’s not a chance that I’ll ever own an S21, unless it’s handed down to me in a few years time. Not helpful to the OP, I know, but I’ve always been served well by keeping things simple, straightforward and tested.
Dirk, I was responding to Ralph’s comment about needing a datacenter.
I’m also of the view that a number of the issues people have is also related to network setup, not just Android OS.
From your comment, my point wasn’t clear. Most people’s networks share bandwidth not only on external internet traffic, but also traffic within the network - streaming from media servers e.g. Plex, IP cameras, smart home automation etc.etc. With a less than ideal network setup, it’s easy to run into bandwidth limitations, latency issues etc.
If you stream from Qobuz to Roon with bandwidth Y, your internal bandwidth requirement is N x Y, where N is the number of devices playing the same stream.
In the main, I’m talking about wired ethernet. When it comes to WiFi, all bets are off. Competing with interference on the same channel with your next-door neighbour’s WiFi, or you WiFi direct enabled network printer broadcasting on the same channel (I know from bitter experience) loss of signal through walls, reduction in bandwidth with distance from the wireless router/access point etc.
They have plenty of different Android phones, the problem is in the interaction between (some) Android network stacks, (some) routers and switches, and (some) cores, which makes the issue extremely difficult to replicate. For instance, when I had it some years ago, I had Roon engineers doing packet traces in my home LAN (not one of my currents ones), and it was still too fleeting to catch reproducibly. Then I turned IGMP snooping off on a Netgear managed switch, and the problem went away for good. Now I have managed switches again (UniFi), no problem.
I learned this lesson as an early Galaxy S5 adopter. In the first few days, I could literally watch the battery drop from full to empty over the course of an hour and the handset grew correspondingly hotter. Returned it and bought a Sony phone instead.
I have a note 20 Ultra and a Tab S7+ now and neither of them are giving me any concerns at all.
Graeme
I remember the same with my S4, got difficult to hold at times especially when you were charging it and the battery was still going backwards 
Last phone I remember getting like that was the S6, though I have not had a samsung phone since the S4
Well, the update to Roon 1.8 fixed the Android connection problems, Roon wakes up and connects within 1 second to the core.
Samsung Note 10 + 5G, latest OS whatever it is.
It will be interesting to see if the general level of people with this issue reduces. I do hope so.
Mike
Agreed.
We have 3 Huawei android in our house.
Two on android 10 and one on android 9.
All 3 connect to 1.8 on ROCK much smoother & faster than before.
Very happy with the 1.8 experience 
This is good news for many new user’s in particular.
Mine have always been fine since I learned the tricks, but better to not have to know them
Mike
Подтверждаю, Самсунг А7, стал подключаться быстро, на предыдущей версии это была головная боль
Еще один довольный клиент! 
Don’t pop the champagne just yet. Mine worked pretty well for the first 24 hrs, now it has lost connection and it can’t find the core for the past five minutes and counting.
Yup, my Huawei P20 pro just stay at the roon startup page. It works intermittently only. Wonder why it is so difficult to fix this by Roon.
Still stunned here, S10 takes less than a second and Roon found where it last played. The champagne is still being chilled…
Champagne still chilled cause the Roon core cannot be found. Back to crap again.
I had a glitch with mine yesterday. Note 20 Ultra was taking forever to connect.
I uninstalled and reinstalled the controller App on the phone, then got a notification that the core needed an update when I restarted the App. Core updated and all’s well again. I did have to go back into my phone settings and stop the newly installed App from being put to sleep again.
I guess Roon is starting to push out fixes for some of the reported bugs.
Hi have a look at this thread and read through the information there.
It has helped people in other threads who have followed the advice.