When restoring the joomla 3.4 site to the joomla 3.6.5 site
That's… that's not how it works. When you restore a site you are overwriting the site's files and database. You are not transferring content. It is also a SPECTACULARLY BAD idea mixing files from two different Joomla versions. It mathematically leads to a broken site and I've got a very clean warning about this in the documentation since the Joomla 1.5 /1.6 times fifteen years ago.
Here's how it works.
You restore the Joomla 3.4 site into an empty subdomain.
You upgrade any extensions, and maybe PHP if necessary.
You take a backup.
You upgrade to Joomla! 3.6.
You take a backup.
You upgrade any extensions and maybe PHP.
You take a backup.
You upgrade to probably 3.8 or 3.9 (because a jump to 3.10 will likely be way too much).
You take a backup.
You upgrade any extensions and maybe PHP.
You take a backup.
You upgrade to 3.10.
You take a backup.
You upgrade any extensions and maybe PHP.
You take a backup.
You upgrade to 4.0 (because a jump to 4.4 will probably be too much).
You take a backup.
You upgrade any extensions and maybe PHP.
You take a backup.
You upgrade to 4.4.
You take a backup.
You upgrade to 5.0 (because a jump to 5.3 will probably be too much).
You take a backup.
You upgrade any extensions and maybe PHP.
You take a backup.
You upgrade to 5.3.
Obviously, if an upgrade fails you download the backup, clear the subdomain, restore the backup and now you're back at the immediately previous step before running the failed update. Fix any problems you had, take a new backup, and retry the update. Rinse and repeat until the update actually works.
I will have to say this again, even though it's falling on deaf ears. Waiting 13 years for an upgrade is by definition going to be painful, no matter if you use Joomla or WordPress. Three years is probably the longest you can go before a complete rebuild is becoming less trouble than trying to upgrade something across long-obsolete versions of your CMS, your extensions, PHP, and MySQL.
The best thing you can do is small, incremental updates every 6 months at most. Keep up with the new versions of extensions, the CMS, PHP, and MySQL. The time you will spend is a tiny fraction of the colossal amount of time you will burn trying to upgrade a 10+ year old site. When you're trying to go from the Stone Age to the Space Age it's always gonna be painful and have a very low probability of success.
Nicholas K. Dionysopoulos
Lead Developer and Director
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