This happened to me on 4 different accounts at the same time when I left them idle too long and they logged themselves out on Runelite client. Using mobile hotspot solved the issue for me. I think it's a generic connection error, just stop trying log in from that IP for a day and it should resolve on it's own, atleast mine did.
Thank yall for your answers. In the end everything was solved in 2 days or so, the thing was that 3 people were trying to log in at the same time in the same account but yeah thanks again