Constant event id 9646 error with one event id 2915---A couple exchange 2010 servers have these errors---not sure what to make of these errors

I have one 2915 event id but continuing to have constant 9646 event id on a exchange 2010 servers.  I checked other exchange servers and only one other exchange 2010 has constant 9646 errors.  We have many other exchange 2010 servers which do not have these 9646 errors.  Not so much worried about the one 2915 error but and wondering about the constant 9646.  I believe these are related to throttling errors but we are NOT using the default throttling policy.

2915 event id error

Application

MSExchange ADAccess

Process Microsoft.Exchange.RpcClientAccess.Service.exe (PID=6608). User 'Sid~DOMAIN1\user12345~RCA~false' has gone over budget '151' times for component 'RCA' within a one minute period. Info: 'Policy:DefaultThrottlingPolicy_f56cd4fb-41f2-4fe0-b2ee-b29c46bc9c96, Parts:MaxConcurrency:150;'. Threshold value: '100'.

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Event id 9646

Application

MSExchangeIS