How long is it between restarts, is it around 3 minutes (you say a few, just trying to clarify)? If so I would check to see if you’re getting any panics in the logs. If you go to Settings > privacy> Anayltics> Analytics data (the exact names may vary depending on exactly what version of iPadOS/iOS you’re running, but it should still be essentially the same verbiage). Scroll through the list of logs and see if there are any with the name panic.full. If so, click it open and just skim it.
Many times this sort of reboots after a few minutes errors are due to the device not receiving check ins from a specific sensor (the panic will usually read as a watchdog timeout error and give you details about which sensor is not checking in). I am not sure that this affects iPads as much as iPhones, but the behavior is similar enough that I would still check. Even if it’s not this error, looking for panics could help narrow down the issue.