During the last Dynatrace Managed update, I observed an issue with disappearing configuration elements for two of my clients. For example, after the update, one client's Custom Services configuration disappeared, and for another client, the XHR monitoring configuration vanished.
I noticed this problem with version 1.274.157. I have reported the issue to support. I'll keep you posted if I learn anything new. Please be cautious.
Did you tried to downgrade the JS agent to the one before latest, in order to check if the new JS agent version is the RC?
The reason I suggested to try downgrade the JS agent version was, because we had the same issue (losing XHR action) after upgrading to Managed 269. While waiting for support answers, we downgrade the JS version to 263 (latest that support IE7-10) and that solved the issue of missing XHRs. Then we found out with support that there was a use of old Angular that is not support by JS agent version 265 and on.
This is a different situation. In my case, it looked as if various configuration elements were spontaneously disabled after a cluster update. the XHR was switched off, data collection stopped. After re-enabling the configuration, everything returned to normal.
I have never encountered a similar situation in DT.