Tried to make my own modpack using mods on Aternos. I believe that some of them are the wrong version but here's the log.
The most common error I saw was this:
[21:02:16] [main/WARN] [mixin]: Mixin config mixins.phosphor.json requires mixin subsystem version 0.7.10 but 0.7.4 was found. The mixin config will not be applied.
