I've seen similar issues in the past, usually related to issues within the software. Last time I had an endpoint restart mid-call, I was running TC7.3.2 and it was due to incoming audio packets, fix for it was in TC7.3.3. What software version is the EX90 running? Can you give us more information and details as to what is happening, when it's happening, etc?
You're running the same software version that I was when out endpoints would intermittently restart during video conferences, recommend you upgrade to TC7.3.3 or even to the latest version which is TC7.3.12.