Troubleshooting a Modded SE Fightstick

When I quickly move the stick from forward to down/back on either side, the stick temporarily becomes unresponsive and I’m stuck in the down/back position. For example, if I’m playing Bison, and attempt something like HK scissors, FADC c.LP, st.LP I will be unable to stand up for the st.LP. This does not just happen with double taps. Any time the stick is held in the forward position, then quickly returned to down/back, the down/back input sticks for about a full second.

Solutions already attempted:
Fiddled with the harness connection.
Removed Sanwa stick and put in the stock SE stick. Same problem persisted.
Put in brand new wiring harness. Same problem persisted with both the SE stick and the Sanwa stick.

Parts in stick:
Sanwa JLF
Seimitsu screw-in buttons.
Everything else is stock

I hope someone can help. As of right now my Street Fighting days are over unless I find a solution. :[

Thanks in advance. Any replies are very much appreciated.