Server's just running out of ram too often, no way out of it truly except upgrading.
However, here's a list that may prolong the issue
Delete some plugins
Delete some worlds
Limit your worldborder
Limit mob spawns
Limit view distance on your server
However, the most effective way will always be to upgrade your Minehut plan to include more ram. You're just running out of memory, too many worlds or plugins or players will do that.
If you're somewhat experienced, you can also tweak the paper/spigot settings to squeeze the most out of your server by following this guide: https://github.com/YouHaveTrouble/minecraft-optimization