This post is mostly for techs or people with advanced knowledge, situation is as follows.
Fritzbox 1 - Had issues with this rebooting constantly, it was sent in for testing and failed during their testing and never turned back on.
Fritzbox 2 - Ok for the first week (this was 6 months ago), then had issues with it rebooting, and another issue with the phone line staying connected for around 6-8 hours then going to no dial-tone at all. It crapped itself last week when it was rebooting 13 times a day so we sent it in for a test.
Fritzbox 3 (Temporary replacement) - We have this while they were testing number 2 and it has rebooted a couple of times, although not as often as number 2 was happening. Can't tell if issue with phoneline is gone because phone number hasn't been setup on it.
Snaps diagnostics = They found no fault with Fritzbox 2 and also there's nothing they can pickup with the line (extended line tests multiple times) at my house aside from some errors which the fritzbox's are automatically correcting.
Suggestions were to change the power socket (already tried, also I don't see how this would be effecting it since we have other things like (servers/wireless router/etc) attached without any issues and to maybe get a sparky to come look at the wiring in the house.
I'm not here to complain, just to see if anyone can think of anything else that may be causing the fritzbox itself to reboot (this is confirmed by the logs getting cleared).