Sourabh Agarwal announces a new tool to determine why your Availability Group failed over:
The first step in using the utility is to configure the configuration.json file to include the location of the data files and the details of the availability group for which analysis is being done. For a correct analysis, all replicas in the availability groups needs to be listed in the configuration file.
The next step is to capture the various logs from each of the replicas and add those under the data folder. The following files are required for the analysis.
SQL error logs
Always On Availability Groups Extended Event Logs
System Health Extended Event Logs
System log
Windows cluster log
This looks interesting.