Well done for trying experiments so far.
One more perhaps? 1. Make a new machine that is also 1.8.19. 2. Restore the dump file into that. 3. Upgrade that Subversion to 1.9.7 - following advice in the release notes for repo upgrades too 4. Make a dump file again on that new machine. 5. Try to restore that new dump file to the *intended* 1.9.7 machine.
