Thank you for the crash logs! I finally have an idea why it happens (2 or 3 minutes) after startup: One of the recent versions introduced automatic blockchain saving through the RPC every 2 minutes, and that can take more than 30 seconds (which is the WebRequest timeout I was using). I have set the timeout to Timeout.Infinite, as local requests may take any seconds. The reason why I didn't encounter this issue is that I am using an SSD, thus, my read/write times are faster than in the case of HDDs. (Probably, that's the reason behind TheNobodies' server being able to handle the situation without crashing.)

Also, I made the blockchain save only every 5 minutes instead of 2, but the wallet will still save every 2 minutes (as that's a lightweight operation compared to storing the blockchain).