How do I fix this without upgrading versions?
I just did a quick test with 2.9.0.
For me the sync worked. A quick fix for you would be to close electrum, delete the content of electrum_data except electrum_data/wallets (also a backup won't hurt) and start electrum again.
However, as @pooya87 wrote, there are cases the old client doesn't know how to handle and the sync will keep failing. And then you'll
have to upgrade (I see no valid reason for keeping that outdated and dangerous version, really).