[EDIT] I just solved the problem myself, but since this took me hours, I will still post this should anyone have a similiar problem, and because I am still not sure that this was all there was to it.

The solution was to switch off one of my converters and let it cool off for half an hour before switching it on again. My setup might be rather rare considering these converters are not sold anymore a lot (I have 4 Swissonic AD24 8 channel analog to ADAT converters on one Raydat, and 1 (apparently faulty) on a second Raydat), but I would not have guessed that a faulty input of an ADAT source could impact the whole sound stream across the bus and cause a lag on channels that are processed by a different PCI interface. Somehow the sync data in the ADAT stream must have corrupted the sync.

If it did that.

So here's the post:

Hi, after a Windows 11 install from scratch, I have a heavy lag.

If only one Raydat card is working (by enabling 'ASIO 32 channel-limit' under the global tab in rme settings; I know the other card works still, but FL Studio will not show channels for the second Raydat if it is disabled), everything is fine with no lag at all.

If I have both cards visible in FL, I get a heavy lag of about half a second playing my synths.

What might be notable is that whatever comes into the second Raydat also has lag, but less than Raydat 1.

And when I start FL, the whole system sound (if I have youtube playing in the background) will also skip half a second.

I mention these oddities because I really have no idea what to look for.

Under Windows 10 everything was ok, all connected converters and Raydats ran flawlessly.

I almost wanted to delete this post just now, when suddenly it all worked again. In FL, I switched playback tracking in audio settings to 'driver', then all adat channels were lag-free for a whole minute, until I set the input of one FL channel to a certain ADAT channel, which made the lag appear again. As if the sound stream was somehow unstable.

I hope I am making myself clear. Is it some windows performance setting? Another FL Setting?

I would have asked in a FL forum, since in totalmix the lag is not there. Only if I start FL Studio, everything starts lagging (including yotube). But I am convinced it is a driver issue because the different Raydats behave differently.

The next idea was to take the second card out again, boot, shut down, then put it back in and see if that fixes it...

On top of everything one of my converters just bade farewell, so I won't need the Raydat for the moment... No need to hurry with any helping thoughts... Which I would still be grateful for! Thank you very much.