Found another post on the steamcommunity page:
https://steamcommunity.com/app/392110/discussions/0/1741090847740290320/

I have noticed this too and been too lazy to make a bug report. Thank you.

Edit:

I tested multiple times in Debug Mode, I cannot pin point why this happens it seems to happen at random. I tested 6 times @ 150 turns w/ similar results. No matter what I test they seem to just randomly stop working after a certain period of time. 2 of the 6 times the Juggernauts never worked properly - 3 of the 6 times it happened at random (first working normally and then breaking sometime within the game) - 1 time out of 6 they did not break at all within the 150 turns.

• Single.sav
• Summary / Title: Juggernaut only fires the large hardpoint.  No other weapons will fire.
• Description: Upgraded my Military behemoth to juggernaut and it will only fire the large hardpoint.
• Steps to Reproduce: Attack anyone.  You can edit the ship and when moving weapons between hardpoints, only the large will fire.
• Reproducibility: 5/5
• Expected Behavior: All weapon slots actually work.
• Version: 1.3.14 S5 Gold-Public
• Notes

So I pulled my Juggernaut out of its fleet and let it fight by itself.  I did see its bombers attacking and had the visual for the Heavy Mount firing.  No other weapons showed firing but the after battle advanced info did show damage from the other weapons installed on the Juggernaut.

It appears it does damage but just no visuals.

Please get this resolved.

Thank you.

During my multiple tests there was no damage at all from other modules, double check ur statistics ensure both ur Bombers and Heavy Mount are of same type so it doesnt lead to any confusion -> i.e. both Projectile

Can you post screenshots of your after battle summary screen, because in every test No other Mount did Damage aside from Bombers/Fighters and the Heavy Mount. I did 6 independant tests.