Describe the bug
I attached screenshot. Check there please.
and also, checked with other mods, and there is no bug like this.

To Reproduce
Steps to reproduce the behavior:

1. Open backpack
2. Press shift to see backpack's inventory and compare

Expected behavior
Just working correctly.

Screenshots

(Sorry for korean,)

Versions
Mod version that you're using. Version of forge may also be helpful in some cases
sophisticatedbackpacks-1.16.5-3.11.1.390
EquipmentCompare-1.16.5-1.2.7

#313 maybe same issue.

Alright this will need to be reported to EquipmentCompare, they don't seem to be compatible with forge's events that allow mods to implement their own handling of tooltips.
I am not expert on mixins but it may be because both them and forge are adding functionality in the same part of vanilla code and I guess their doesn't get added to the correct part. Anyway they should be using what forge has ready for them instead.