My WAC Server was working for the past 2/3 months and just few days ago started getting error message simlar to the ones posted above.
In the logs files I get the following errors:
11/28/2022 16:23:58.78 w3wp.exe (0x0C20) 0x3DA4 Office Web Apps WAC Hosting Interaction adhrj Monitorable HttpRequestAsync (WOPICheckFile,WACSERVER), request failure [HttpResponseCode:NotFound, HttpResponseCodeDescription:Not Found, url:http://spserver:port/IT/_vti_bin/wopi.ashx/files/8d7c0cb9ac1a47398f62fefb3120d9e5?access_token=REDACTED_1064&access_token_ttl=1669681408139] 2538332f-189a-4c87-ae0b-9a555e31dc3f
11/28/2022 16:23:58.78 w3wp.exe (0x0C20) 0x3DA4 Office Web Apps WAC Hosting Interaction adhrr Medium HttpRequestAsync (WOPICheckFile,WACSERVER) Setting Completion [Time in ms: 30071, Bytes Read: 0] 2538332f-189a-4c87-ae0b-9a555e31dc3f
11/28/2022 16:23:58.78 w3wp.exe (0x0C20) 0x3DA4 Office Web Apps WAC Hosting Interaction ajdv9 Medium HttpRequestAsync (WOPICheckFile,WACSERVER) SetCompletion Track start | setting trackers | WebRequest.Create() | Create() returned | _req.ContentLength 0 | setting request headers | setting user agent | setting keep alive | setting timeout callback | Start calling StartResponseProcessing | StartResponseProcessing._req.BeginGetResponse() | BeginGetResponse() returned | StartResponseProcessing RETURNS | Start RETURNS | End.AsyncWaitHandle.WaitOne() | GetResponseCallback isSync:False | _req.EndGetResponse() | GetResponseCallback WebException | RecordWebException | RecordResponse NotFound | SetCompletion False | 2538332f-189a-4c87-ae0b-9a555e31dc3f
11/28/2022 16:23:58.78 w3wp.exe (0x0C20) 0x2D4C Office Web Apps WAC Hosting Interaction ag7m6 Medium WOPI Http Request Completed [host machine name:, version:, host correlation:] 2538332f-189a-4c87-ae0b-9a555e31dc3f
11/28/2022 16:23:58.78 w3wp.exe (0x0C20) 0x2D4C Office Web Apps WAC Hosting Interaction ajahy Medium Error message from host: Verifying signature failed, host correlation: 2538332f-189a-4c87-ae0b-9a555e31dc3f
11/28/2022 16:23:58.78 w3wp.exe (0x0C20) 0x2D4C Office Web Apps WAC Hosting Interaction agmoa Medium WOPICheckFile,WACSERVER FileNotFound [url:http://spserver:port/IT/_vti_bin/wopi.ashx/files/8d7c0cb9ac1a47398f62fefb3120d9e5?access_token=REDACTED_1064&access_token_ttl=1669681408139, host correlation:] 2538332f-189a-4c87-ae0b-9a555e31dc3f
11/28/2022 16:23:58.78 w3wp.exe (0x0C20) 0x2D4C Office Web Apps WAC Hosting Interaction adhsk Unexpected WOPI CheckFile: Catch-All Failure [exception:Microsoft.Office.Web.Common.EnvironmentAdapters.FileUnknownException: WOPI 404 at Microsoft.Office.Web.Apps.Common.WopiDocument.LogAndThrowWireException(HttpRequestAsyncResult result, HttpRequestAsyncException delayedException) at Microsoft.Office.Web.Apps.Common.HttpRequestAsync.End() at Microsoft.Office.Web.Apps.Common.WopiDocument.GetWopiRequestResultWithRetry(Int32 maxSize, MemoryStream ms, WopiRequest wopiRequest) at Microsoft.Office.Web.Apps.Common.WopiDocument.CheckWopiFile()] 2538332f-189a-4c87-ae0b-9a555e31dc3f
11/28/2022 16:23:58.78 w3wp.exe (0x0C20) 0x2D4C Office Web Apps WAC Hosting Interaction ajjve Medium WOPI CheckFile: Catch-All Failure [url:http://spserver:port/IT/_vti_bin/wopi.ashx/files/8d7c0cb9ac1a47398f62fefb3120d9e5] 2538332f-189a-4c87-ae0b-9a555e31dc3f
11/28/2022 16:23:58.78 w3wp.exe (0x0C20) 0x2D4C Services Infrastructure Services Infrastructure Logging ai94t Unexpected FileUnknownException while loading the app. [FileSourceId: -1088102096] [ClusterId: 0] [ExtraErrorInfo: ] 2538332f-189a-4c87-ae0b-9a555e31dc3f
11/28/2022 16:23:58.78 w3wp.exe (0x0C20) 0x2D4C Office Web Apps Office Web Apps common af46w Medium WACServer HttpModule: Completed request with status code [200] 2538332f-189a-4c87-ae0b-9a555e31dc3f