WordPress and plugins including
Envira gallery stores many options as “serialized data”, which contains both the string content of things and their length. So when you modify the URL and the length changes, then the serialized data is no longer correct, and PHP rejects it.
Serialization has become a standard in many programming languages. The problem with serialization is data portability. Let’s see an example of serialized data in PHP:
If you change your domain, replacing it is not enough. If the old and new domain don’t have the same number of characters, and you search and replace the domain URLs in your database, you could get in trouble and corrupt your content data.
There’s no way to update serialized arrays using just MySQL queries. You need to use PHP, load the arrays, find the values, replace them and serialize back. That’s very tedious and error prone, but there are several tools that help you doing the hard job. My recommendation is to use a plugin that does the complete migration for you. WP Migrate DB, Duplicator, or All-in-One WP Migration are some examples of good plugins for this task, and they take care of replacing the serialized arrays.
For more information, please refer to the link below.
After fixing this issue, you may update your theme and plugins to latest versions.