2D FSI Failed to evaluate reaction forces

Hi I'm performing a microfluidic FSI: 4us analysis

Error: Failed to evaluate reaction forces

COMSOL version 5.3

(See attached geometry and input)

This is what comes out from my time dependent analysis of a layered vibrating membrane, with prescribed displacement of 0.5um, over a fluid chamber, following a rectangle wave. I'm using Generalized alpha solver, 0.001 relative tollerace +0.1 tolerance factor, fully coupled + Automatic Newton, strict time stepping:

range(0,1e-7,7e-7)range(7.4e-7,1e-9,3.4e-6)range(3.5e-6,1e-8,4e-6)

The error comes out after the first ramp, around 1.7 us ( i tried a lot of configurations, at most I reached 1.9 us).

Any suggestions? Thanks in advance.