“Roon Core with Squeezelite Player (Experimental)” is a setup mode on your Innuos device. It is “provided as is and therefore not guaranteed to work reliably” by Innuos, It is known by Innuos that “This Experimental Mode may have occasional dropouts”.
As far as Roon Labs is concerned:
So go into the setup menu of your Innuos product and check there if you use the unsupported mode or not. Change if needed.
No, the DirectStream DAC is listed as a supported Roon Ready device (seems to require the optional Bridge II Network Card though) and Roon Tested device (if you connect it by USB).
As for your current setup, neither the “Phoenix reclocker” nor the “matrix audio spdif 2” are Roon Tested (or the PS Audio DirectStream DAC via SPDIF input if that matters for you). This means that there is no special support offered from Roon Labs for your current setup.
What to do when you have issues with a Roon Core on Innuos devices is documented here:
PS: As others already mentioned, 20k+ albums is not considered a small library (by Roon Labs too).