Same issue with a module for a shopping cart. Currently looking into whether or not this can be easily swapped out in the code, although since the module isn't developed internally, that's likely not going to be an all too easy task.

Would appreciate a fix for this issue.

SELECT ' ' REGEXP '\\{20}'

--> 0 in MariaDB 10.2.2 and Percona 5.6.22-71.0; so perhaps a poor constant?

SELECT ' ' REGEXP '\\x{20}';

--> 1 for 10.2.2, but 0 for 5.6.22 – Suggest you take note of this incompatibility.

Yes. MariaDB uses PCRE and what you observed are the consequences of this fact.

PCRE supports \ddd, \xhh, and \x{hhh} for specifying characters by their codes. That's why you've got a mismatch in first query and match in the second. MySQL and Percona use Henry Spencer's library which does not support \x{hhh} syntax.

It's not something we can fix. PCRE is no longer developed. PCRE2 is the currently supported version, but it still returns the same error, unfortunately.