They (MOTU) are going to have trouble with this, since it is working with most people’s configs. (I have it working well here with no issues other than CueMix’s meters sometimes disappearing. If that is one of your problems, let me know, as I know of a fix for that.)
Initially, I say go to Device Manager and disable “MOTU Audio WAVE for 64 bit” (that is the Windows Audio driver) to see if the crackles go away. That driver is rather notorious if you are running any other software other than a DAW or Cantabile with audio output at a fixed sample rate. That driver in particular throws a hissy fit if any audio with sample rates other than the one it is set for are delivered to it, as it does not handle sample-rate-conversion well at all. (I use Voicemeeter for such occasions in between my Ultralite and Windows.)
Just as another data point I have had a MK4 for 2 years, and 6 months ago also got an ultralite AVB and both work very well. I use most of its I/O regularly and it works as expected.
I use it as our live Foh and monitor mixer with the band along with the behringer ada8200 adat expander.
I generally have reaper for recording or playback, and c3 open for my piano sounds. Sometimes I record 12 stems in reaper and c3 simultaneously using the same Motu ports with no problems. I generally also have a couple of lighting programs open which connect to the same Motu output audio port for sound to light.
I did try voicemeeter a while back just for an evening and didn’t find any issues in that short time.
If just using audio then I run at 128 samples. I generally drop that down to 256 if I use the 2nd lighting program (elm) which is processing video. This is on a 7th generation i5 (u series).
I do notice the difference between 256 and 128 samples.
I use a Motu 624 with thunderbolt(stage laptop) and USB connection(studio PC). Works very reliable on both my Windows 10 systems as well. The ultralite mk4 is running on the same software stack as the avb, 624, 828es, 8a, 16a etc. Maybe this platform is more stable in combination with W10???