Astroid changes -> not saved

Joomla 6.1.4
Template Tp-Gym
Framework Version: 3.5.0
Template Version: 2.7
website: oldenglishsheepdog.eu

When I do any update in the Astroid section I can't save it. Even without updating anything; when I klick the 'save' button, it will keep running for hours without success.
Any other save action in this Joomla environment works properly.

Browser: Safari and Chrome (same issue)
new browser, reboot Macbook: same issue. 

What should I do to make any updates to the Astroid settings? It did work 2 weeks ago. 

Since saving works correctly in other areas of Joomla, but hangs when saving Astroid settings, the issue may be related to a server-side security rule or firewall (e.g. ModSecurity) at your hosting provider. Such rules can block requests containing certain configuration data.I would recommend checking the server error logs and asking your hosting provider to verify whether any firewall rules are blocking requests to Astroid. This would help identify the cause before making any changes to the template or framework.

Hi, thanks for your prompt reply; 
Host is Strato

and attached the server report. (sorry I'm not a wizzkid, just trying to keep my website up to date..)