The log file for ActiveSync and the end customers have never been so quiet

Could someone throw a little light on the only message now appearing in the log

Is it a transient issue that can be ignored or does it signify something more important?

 

[2017.06.02] 09:32:42 [1376697054] System.Exception: Message does not exist
[2017.06.02] 09:32:42 [1376697054]    at MailService.Remoting.Mail.#cqe(String #bab, String #dHb, UInt32 #dqe, Boolean #eqe)
[2017.06.02] 09:32:42 [1376697054]    at MailService.Protocols.ActiveSync.Helpers.SyncEmail.#1ne(String #6j, VersionHandlerBase #yZi, EasFolder #4Db)
[2017.06.02] 09:32:42 [1376697054]    at MailService.Protocols.ActiveSync.Helpers.SyncEmail.FillApplicationData(String itemGuid, SyncApplicationData& ad, Boolean isUpdate, Boolean isFetch, VersionHandlerBase handler, SyncOptions options, EasFolder folder)
[2017.06.02] 09:32:42 [1376697054]    at MailService.Protocols.ActiveSync.Helpers.SyncEmail.GetApplicationData(SyncMetaItem item, Boolean isUpdate, Boolean isFetch)