shield goes invisible sometimes, even if holding right mouse (the shield works, and you are slower, but there is no shield on the screen.

when it happends only restarting helps

Apologies for the late fix, thanks for opening the issue and giving the mod a try! This has been fixed in version 2.0 of Passive Shield.

https://www.curseforge.com/minecraft/mc-mods/passive-shield/files