Frankly, this depends on the design of your electrodes - if you are using an Ag/AgCl in solid (recryst.) KCl then I would expect no problem on behalf of wither the electrode or internal electrolyte. I would be more worried about your electrode casing (deformation or even melting), but with most commercially available SSEs using PTFE or PEEK that should be irrelevant.
High pressure should also not be an issue. If anything, hydrogen sulfide might interfere with an Ag-based electrode, but that would be regardless of pressure and temperature.