After running the tests I managed to reproduce this issue. The issue will occur only if previously the browser has already a JSESSIONID cookie set by other application server (for the same IP/domain). Because the JSESSIONID format is not the same Weblogic will not recognise it and assign another JSESSIONID cookie. Now when any interaction is initiated both cookies are sent, but the first one (set by another server) will be read by Weblogic and since it's not recognised it will throw a ViewExpiredException which eventually is interpeted as a session expiration.
The solution is to cleanup the old JSESSIONID cookie before using Weblogic and everything will work fine from then on.
After running the tests I managed to reproduce this issue. The issue will occur only if previously the browser has already a JSESSIONID cookie set by other application server (for the same IP/domain). Because the JSESSIONID format is not the same Weblogic will not recognise it and assign another JSESSIONID cookie. Now when any interaction is initiated both cookies are sent, but the first one (set by another server) will be read by Weblogic and since it's not recognised it will throw a ViewExpiredException which eventually is interpeted as a session expiration.
The solution is to cleanup the old JSESSIONID cookie before using Weblogic and everything will work fine from then on.