You may find Integrations, such as REST or SOAP Message via MID Server, LDAP or Import Sets etc., which would normal take a second or two, take longer to run than usual. After looking at the ecc_queue Output records, and comparing the Created time with the Processed time, you may see a delay in the MID Server picking up the job of up to around 40 seconds.
This can be a big problem if you are doing the bad practice of waiting in a script for a response to a MID Server job. MID Servers may sometimes take longer than usual, and this causes instance threads to be blocked, which can quickly lead to a backlog and performance issue for the whole instance. RESTMessageV2 allows you to do that, even though you shouldn't. Instead execute the message 'async' and allow your script to end at that point, and write a 'sensor' ecc_queue business rule to read the response instead (which is how Discovery and Orchestration do it).
Helsinki and later, which is when the AMB Channel was implemented, and the default fallback Polling time was set at 40s.
The AMB Channel may have disconnected for some reason. This is the real-time connection from the MID Server to the Instance, which lets the MID Server know when new jobs have been created for it.
The MID Server Agent log will show all instances of when the AMB Channel has had to reconnect, and where it fails to.
08/15/18 21:24:45 (404) ECCQueueMonitor.40 WARNING *** WARNING *** Reconnecting AMB channel.. 08/15/18 21:24:45 (404) ECCQueueMonitor.40 Initializing AMB client... 08/15/18 21:24:45 (405) AMBClientProvider Connecting AMB client to instance... 08/15/18 21:24:45 (468) AMBClientProvider WARNING *** WARNING *** Unable to subscribe to AMB channel: /mid/server/bd27969913068bc036aff4d2e144b0a7
If your timeout set for the job assumes the job will be run immediately, and is shorter than the time it takes the MID Server to notice and run the job, then it will timeout. Otherwise the job will still run, but be delayed starting.
There may be many potential causes of "Unable to subscribe to AMB channel". It could be a problem with network conditions or devices between the MID Server and Instance interfering with the connection/session which would need investigating. There may be exceptions or further errors in the agent or wrapper log of the MID Server that may help explain it.
There have been some known problems with the AMB Channel in general, and specifically for MID Servers in certain network environments which can be seen in the release notes. Most are already resolved for most customers, so it is worth applying the current patch to your instance to discount those first.