Make sure you're using the latest SIGPro release. Then post in our helpdesk to assist you directly.

Have you checked that all SIGPro plugins are published?

(If you have Joomla 3.8.12, I highly recommend you update to SIGPro latest (currently 3.5.0 pre-release) as there are many improvements everywhere, including new gallery layouts...)

I'm afraid I don't see any difference. If the plugins tags still show, something is stopping SIGPro's content plugin from rendering. It could be another extension causing the issues.

If you want to be sure, uninstall SIG Pro and install the free version of it. If the free version does not run as well, then something else is causing issues in the way content plugins are executed.

As for the update, you will have to renew your subscription to get the latest 3.5 version. If you renew your subscription, I can also offer premium support from our helpdesk system and directly debug the problem for you.

The galleries are never lost. That's one of the benefits of using SIG Pro or SIG (free) over other gallery systems. And free is interchangeable with pro exactly so you have a smooth upgrade path if you're coming from the free version.

But you will lose the component settings, so just note them down in case you need to re-install SIG Pro (same or newer version if you decide to renew your subscription).