Latitude E5550/5550 lower touchpad buttons not working

Hello from Germany!

Im running a couple of E5550/5550 with W10/11. Yes, I know, no official support

Since yesterday, the lower touchpad buttons (NOT the three under the space bar) stopped working.
Touchpad and all other TP options are working well.
I changed the SSD from this machine to another E5550/5550 and all TP buttons are working fine. So NO driver problem.
Any idea how to fx this problem?

Best regards
Peter