if you’re using bridge, make sure to increase the block size in your DAW, as this option in Core> Audio gets locked, and is often WAAAAY too low for Rack.
Looks like this is called Buffer Length in FL Studio. Go for a power of 2, starting with 4096, and lower it until you lose stability. Also, apparently there’s a triple buffering option?!? maybe check if that one helps/hinders.
(my source: https://www.image-line.com/support/flstudio_online_manual/html/envsettings_audio.htm)