Website Input: Cannot parse data with custom css selector for apache server-status page

[kenntun]

I would like to crawl data from the following section of the apache server-status page

I used the following css selector to select the section:
table:first-of-type tr:not(:first-child)

The results preview displays what I wanted. However, the app would not let me save the setting, showing an alert "The input could not be saved: An error occurred". What could I do?

[LukeMurphey]

Could you be so kind to take a look at the logs and see what it says? Run the following search and let us know what kind of things you see:

index=_internal sourcetype=web_input_modular_input NOT (DEBUG OR INFO)