As the migration completed, the configuration file
web.config is not updated. The paths defined there remained unchanged, and kept as it were on source server.
That leads to internal server error thrown by the migrated website when browsing it.
The situation was caused by software issue PMT-2286. The fix is planned to be included in one of the future product updates.
At the moment no solution is available, thus the configuration file has to be updated with correct paths on destination server manually.