This is something I spent quite a bit of time debugging after it kept popping up intermittently. So I thought I'd post about it here in case it helps anyone else.
Running "Clear-EventLog" system in powershell causes all IMAQdx connected hardware to disappear from NI MAX and it's inaccessible until you restart the system.
Clear-EventLog system
We noticed the issue when our systems stopped working after a certain deploy script was run (the deploy script was clearing system logs). Subsequently we had to manually restart all systems before they would work again. It turned out to be due to this one-liner in the deploy script.
I guess IMAQdx devices get enumerated at startup and stored in system logs, if the system logs are cleared then the devices disappear!
