The 3.5mm plugs act wonky sometimes. Even when new. Many people moved away from the 3.5mm to other types of connectors. I believe @Diamond1 has had very good results with aviation connectors. Maybe he will comment.
I had the exact same issue with my probes using the 3.5mm plugs. I would have to wiggle them around, pull them out a little, push them in a hair, etc. God forbid I move the box because then I would have to fine tune the plugs again! I went with screw terminal plugs. They are bulky but they are super solid and its fast to switch out or add probes without soldering.
https://www.amazon.com/gp/product/B01MZHXKN2/ref=ppx_yo_dt_b_asin_title_o06__o00_s00?ie=UTF8&psc=1