I removed Spartan Foundry and it broke all my skips and storage containers, saying there was a 0kg mass limit and that's why you couldn't store more than 1 item, causing it to kick out any other item that was there.

I restored the previously removed mod into the correct spot and loaded a save before this bug occurred and everything is working correctly now.

LWM did mention that there is a "Check for Storage Being Over Capacity" option in the mod settings.

There's also the option at the bottom which allows you to edit the settings of each storage unit. Enabling and disabling that will reset everything to default values. Since this bug has to do with max mass limit, this is probably the correct solution.