Foglight for Webmonitor is generating false alerts. There is 'Expected Content' configured for that Transaction. So if the specified text is not present on the web page, then the 'WebMonitor Transaction Availability Check' rule on the FMS will trigger. The rule fires at the 'Warning' severity level, not the 'Fatal' level.
The 'Performance Browser' FMS web UI page says that this Transaction's 'Service Availability' is 100% and its 'Page Availability' is about 50%. Those readings indicate that, though the web page used by that Transaction is not down/ is accessible, the web page is missing the 'Expected Content' for about half of the Collections (access attempts). (If the Transaction / web page had not been accessible, then the 'Service Availability' would have been 0% and the rule would have triggered at the Fatal level).
We checked the web page, however, and it does have the Expected Content.
It could be that the web page configured as that Transactions that is triggering the alarms, has inconsistent behavior. If that 'Expected Content' is sometimes present on that Page, and sometimes absent on that page, then that would explain what you are seeing. The rule/alarm is firing for the times when the 'Expected Content' is missing.
One way this could happen is if there is redirection _sometimes_ occurring for that page. That sometimes when you access that URL in a browser, you get a web page returned from the server that has the expected content. And sometimes, for that exact same URL, when you access that URL in a browser, it redirects to a direct URL / web page that does not contain the expected Content text.
If the situation described above is occurring, then Webmonitor is working as expected. This is not a false alarm afterall. WebMonitor has done its job well here. It has alerted you to a real problem with that webpage.