Firing at-4 and panzerfaust Freezes the Game

[Matcha7]

Describe the bug

Upon firing the at-4 rocket launcher and the panzerfaust, the gun drops to the ground and a weird animation is drawn repeatedly causing the game to slow down. FPS is dramatically reduced. Also, there is no reload animation for these two weapons. Please see the attached screenshot.
To Reproduce
Steps to reproduce the behaviour:

1. Fire the at-4 or the panzerfaust

Expected behaviour
Rocket launches, blows stuff up (like other rocket launchers ex. RPG seems to work fine)

Screenshots
https://i.gyazo.com/8565333d2ea55bd50382aa254249a6b3.png
https://i.gyazo.com/18f5e7b5e79ef47e0da8a71d5939bcd8.png

Versions (please complete the following information)
Forge: 1.12.2 - 14.23.5.2768
Flan's Mod: v5.6-beta.6

Additional context
It is possible that the bug is client-sided. Testing this bug on my flans mod server: I used another computer (one that the server isn't hosted on), the bug would occur causing my client-side FPS to drop. I quit the server and relogged and the animation/bug is no longer there. Does not seem to crash the server, but the bug happens every time I shoot the gun through my client.

[Zl0gix]

the LAW rocket launcher does the same thing