Today I found a solution to log in after trying for hours and days in vain. Also with the help of Migros Bank Support. As you know, I switched to the new browser-based e-banking system about 10 days ago. After it worked for a few days, it suddenly stopped working. On another Blackberry device (fresh after a reset) the procedure worked without any problems. So it had to be this one device. Here is the solution: I used Settings / Apps and notifications / Show all apps (at the bottom) / Blackberry Launcher / Memory / Clear cache / Clear data to clear the cache and data. After a restart it suddenly worked.