If some requests from MapSVG to the server are failing without any obvious reason,
it could be caused by the
mod_sec Apache's module that blocks suspicious requests.
What you can try to do first is disable
mod_sec entirely and see if that helps.
If it does, check the
mod_sec logs and find the reason of the blockage.
When you find the reason, you can change mod_sec setting to prevent the blockage.
How to disable
mod_sec: add the following lines to the
.htaccess file in your WordPress root folder:
<IfModule mod_security.c> SecFilterEngine Off SecFilterScanPOST Off </IfModule>
The method above may not work though. If you have a control panel on your server, it may be possible to disable mod_sec there. If you don't have a control panel, try to google how to do disable mod_sec on your server OS.
If you have enough experience, you can try to disable the following mod_sec rules: 340155, 380023, 341155