Hi Ryat, thanks for your answer.
I had read the post you mentioned before I started my thread. I started my own thread because the problem discussed in the thread you linked sounds similar but still different to my specific issue.
Yesterday I tried to reproduce the issue and did exactly the same thing that i had done before the issue became present (unplugged the modem from the router and connected the modem directly with my PS4, played online for some hours and then replugged and restarted everything)
This time only the protocols / logs were deleted, but not the Admin password.
Your presumption concerning the "batteries" sounds plausible to me, I think the router is about 5 years old, could be 4 or 6 as well, though.
