Microsoft SQL Server 2012 Mirrors Go Into Disconnected
I experienced very similar issue in my previous company. Database miroring was periodically getting suspended with the same error as you are getting. Mirroring never ever reconnected on its own, but usually I was able to resume it using:

ALTER DATABASE &lt;Database Name&gt; SET PARTNER RESUME


After a few weeks we figured out that even though there was enought memory on the server and enough memory was allocated to the instance our workload was very unevenly distributed and sometimes 100% of the memory was used. Since most of the time we had enough memory we were not authorised to purchase more. I ended up increasing buffer pool extension file and placing it on one of the SSDs which happened to have enough empty space to accommodate it. The problem with mirroring never returned again. I cannot guarantee that the same will work for you, I am mainly sharing my experience.