Titan Mobile DMX input

[gis]

I was testing our consoles after Titan 10 upgrade, when I realized one XLR on one of our Titan Mobile doesn't work properly as input: triggering anything from that input translate in hiccup behaviour.
The same XLR works smoothly as output.
I tried rebooting, reloading session, rewriting triggers, use a new session, but XLR D sometimes get stucked for a split second. This happens only with that console on that XLR. I also exchanged cables and consoles.
I then tried deoxidising pcb near RX4 since there was some dirt (flux? condensation?), I checked for continuity between XLR pins and pcb, I tried swapping ICs: U9 and U14, RX3 and RX4, DIR3 and DIR4.

Still the same erroneous behaviour.

Any hint?

Thanks, bye
G.