Setup a trace using profiler and see what's causing it.

You can set a session timeout to greater that 10 seconds in AG properties.
https://social.msdn.microsoft.com/Forums/sqlserver/en-US/de428459-f8c1-4e66-b712-8367cf455107/changing-the-session-timeout-in-an-availability-group

Which quorum settings are you using?

You will see "backupthread" waits during restores and backups. It all depends on your database size and if you are using compression.

You can check the progress of the...

myNumeric                             
845.53   

myDecimal
525.34

You don't need an error when extra digits are...

Matt
Can you describe your always on setup in your 10 SQL instances?

Have you tried using
IF fn_hadr_group_is_primary('AG_Name') = 1
    BEGIN
        "YOUR SQL HERE"
    END
ELSE
    BEGIN
        PRINT 'This is not the primary replica - exiting with success';