ive used the blackface apollo 8p via thunderbolt 3 and faced many issues, mainly dropouts in cakewalk. I couldnt figure out why, ive tried all buffer sizes, windows optimization and bios changes to no avail. Email UAD support and they couldnt help much too. Could be an isolated issue with my PC but ive since sold that apollo and gotten an RME UFX+.
Also WDM drivers are really bad that causes lots of crackling when playing audio from your browser etc. Also, the bad wdm drivers causes your recording source to be badly distorted when using the apollo with discord or skype etc.
You can read several issues in their bug reporting forum
Sources:
UAD WDM Drivers issue (first reported in 2017 in the first link): https://uadforum.com/support-troubleshooting/30545-apollo-8-thunderbolt-recording-crackle-sound-non-daw-apps-problem-windows-10-a.html
https://uadforum.com/support-troubleshooting/40666-apollo-thunderbolt-wdm-issue-ever-fixed.html https://uadforum.com/support-troubleshooting/42211-windows-audio-crackling-randomly-possible-solution.html#post290032
UAD Arrow WDM crackling (supposed fix): https://uadforum.com/support-troubleshooting/43635-amazing-solved-crackling-distortion-windows-44-1-48khz-100%-working2019.html