Hi, @ThierryEscande, thanks for the input here。

It is pretty interesting that I kind also located the same place by following the interrupter path.
https://github.com/liayan/xen-xcp-ng/blob/main/xen/common/domain.c#L250

It quite fits our case atm that issues happened after hitting the limit of 64. Unfortunately, I can not test it yet because our host is stuck in a weird POST status. Will update here later.