Issue – Replication Log Reader agent was failing with below error messages.
2018-04-24 19:33:07.854 Status: 32768, code: 53044, text: ‘Validating publisher’.
2018-04-24 19:33:07.873 Status: 4096, code: 20024, text: ‘Initializing’.
2018-04-24 19:33:07.873 The agent is running. Use Replication Monitor to view the details of this agent session.
2018-04-24 19:33:07.879 Status: 0, code: 20011, text: ‘The process could not execute ‘sp_replcmds’ on ‘xxx’.’.
2018-04-24 19:33:07.879 The process could not execute ‘sp_replcmds’ on ‘xxx’.
2018-04-24 19:33:07.879 Status: 0, code: 15517, text: ‘Cannot execute as the database principal because the principal “dbo” does not exist, this type of principal cannot be impersonated, or you do not have permission.’.
2018-04-24 19:33:07.879 Status: 0, code: 22037, text: ‘The process could not execute ‘sp_replcmds’ on ‘xxx’.
Resolution – In order to resolve the issue; please ensure database owner is valid.
In my case Publication database was not having owner assigned but this issue might occur if owner is not valid
e.g. user as owner and his domain account is disabled
disabled sql user
Learn Sql Team 
Thanks, I encountered this error and you post helped me found the problem.
The database owner was an AD user that from some reason got disabled.
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Thanks a lot. It helped to fix the issue.
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