Derailleur lowering for a split second while using a specific gear

Hey y’all,

I’m getting this issue where the derailleur lowers for a split second while using a specific gear, no idea what causes this. It feels like some sort of mini skip or tension loss when cycling. Hopefully someone can shed some light.

I’m not super knowledgeable but if you need additional info let me know I’ll do my best.

Thanks in advance.