Erik Kostson
Ansys Employee

These type of problems are very hard to get to converge. Peter has given some very good tips.

On top of that it seems that the material Young's modulus is quite low, so I would start with a lower pressure and see that works (say 10Pa or even 1 Pa).

Furthermore one might need:

Under Analysis Settings, turn on Auto Time Stepping, with Initial and Minimum Substeps to 200, Maximum to 2000.

This will allow the membrane to build up out of plane stiffness gradually - very important.