Well as I was here from 2017, I know a lot of quirks of SLM from way back.
I will update Slimcoin AIO package for Windows. As I see my old package doesn't work anymore, probably due to new version of client.
Still those synchronization is pain in the ... Ah, if it would really get an update to anything newer than this 0.5 btc codebase, it could at least be somehow functioning without hiccups.
I think you'll need to compile v0.6 if not I should have a compiled version (I can send it to you if you need me to).
An upgrade is indeed needed, that's the key issue we have to solve.
I have 0.6 version from compiled by Graham.
Besides is there still problem with mining on 0.6 version? I had such problems when I tried it 2 years.