Hello @gonzalo43tech ,
I’ve also tested on WP 5.4.2 and I am not able to replicate this issue.
In this case, I recommend a plugin conflict test. To perform a conflict test please follow the steps from the flowchart:
https://premium.wpmudev.org/wp-content/uploads/2015/09/Support-Process-Support-Process.gif
If you have access to a staging site it is better to perform that test there (if there is no staging, make sure to make a backup of your site before doing any changes).
Nevertheless, I strongly suggest updating WordPress to the latest version.
kind regards,
Kasia