Streaming lagging suddenly

We have the following setup :
7 cameras, all streaming on 3 different resolutions sending RTSP to the wowza streaming engine sitting in our EXSi server.

Everything worked well for 3 weeks, then all of a sudden, the streaming started lagging.

I restarted the server and the application via the Wowza manager UI, but it did not help and when reconnecting the streams I noticed that with anything below 10 streams , I see the video smoothly in the test player, but when I add streams, everything starts to lag.
We use secure URLs

Any idea what could be happening ?

Sounds like your ESXi VM is at max capacity. I’d start by monitoring the server stats (CPU usage, Java Heap size usage) and checking the logs for any indicators (note that some messages may not be logged as WARN or ERROR but can still indicate a server overload, e.g. messages about skipped frames)