SSRS Performance degradation

I have a fairly busy SSRS Instance and the redering performance is consistently degrading to the point where we have set the recyle time config to 60 as work around and im still getting significant reduction in rendering performance within the hour. once the 60 minutes passes the performance goes back to an acceptable level and begins to degrade once more.

I have played with the memory settings within the config but it doesnt seem to have made a difference. The server is dedicated to SSRS and there doesnt seem to be any memory pressure. at this second theres 32gb of memory and 28gb free with SSRS using around a gig.

Looking in the log we have a lot of the following error

httpruntime!ReportServer_0-193!2b84!05/17/2018-15:14:52:: e ERROR: Failed to 
create worker request: pipeline=0x56C27945E0, exception=Microsoft.ReportingServices.Diagnostics.Utilities.ReportServerHttpRuntimeInternalException: An internal or system error occurred in the HTTP Runtime object for application domain ReportServer_INST130_0-193-131710375157483972.  ---> Microsoft.ReportingServices.Diagnostics.Utilities.ReportServerHttpRuntimeException: An error occurred in the HTTP Runtime object for application domain ReportServer_INST130_0-193-131710375157483972. Most likely, the HTTP request contains an unsupported verb or invalid syntax.
rshost!rshost!2b84!05/17/2018-15:14:52:: e ERROR: HttpPipelineCallback::SendResponse(): failed writing response.
rshost!rshost!2b84!05/17/2018-15:14:52:: e ERROR: Failed with win32 error 0x10DD, pipeline=0x00000056C27945E0.
httpruntime!ReportServer_0-193!2b84!05/17/2018-15:14:52:: i INFO: RsHttpRuntime::ProcessRequest(): calling EndOfRequest() from exception handler of worker request constructor. Runtime=ReportServer_INST130_0-193-131710375157483972. Pipeline=0x56C27945E0.
rshost!rshost!2b84!05/17/2018-15:14:52:: e ERROR: Failed to process request 0x800710dd, pipeline=0x00000056C27945E0.
library!ReportServer_0-193!2218!05/17/2018-15:14:53:: e ERROR: Throwing Microsoft.ReportingServices.Diagnostics.Utilities.ReportServerHttpRuntimeException: Unsupported HTTP verb 3., Microsoft.ReportingServices.Diagnostics.Utilities.ReportServerHttpRuntimeException: An error occurred in the HTTP Runtime object for application domain ReportServer_INST130_0-193-131710375157483972. Most likely, the HTTP request contains an unsupported verb or invalid syntax.;
library!ReportServer_0-193!2218!05/17/2018-15:14:53:: e ERROR: Throwing Microsoft.ReportingServices.Diagnostics.Utilities.ReportServerHttpRuntimeInternalException: Failed to fill worker request, Microsoft.ReportingServices.Diagnostics.Utilities.ReportServerHttpRuntimeInternalException: An internal or system error occurred in the HTTP Runtime object for application domain ReportServer_INST130_0-193-131710375157483972.  ---> Microsoft.ReportingServices.Diagnostics.Utilities.ReportServerHttpRuntimeException: An error occurred in the HTTP Runtime object for application domain ReportServer_INST130_0-193-131710375157483972. Most likely, the HTTP request contains an unsupported verb or invalid syntax.
   at ReportingServicesHttpRuntime.BaseWorkerRequest.FillWorkerRequest()

I have been looking into this on and off for a while and im coming up blank.

Try turning on the Report Server HTTP Log.

You can then cross reference when the error occurs in the trace log, with the request that was logged in the HTTP log. Note that the timestamps in the trace log use local time, while the timestamps in the HTTP log use GMT.

I have the same issue as you and found that unsupported verb was OPTIONS, which looks like it is being sent by a Microsoft Office application:

11/21/2018 22:04:17 xx.xx.xx.xx DOMAIN\user xx.xx.xx.xx 20480 ssrsServer OPTIONS /Reports/Pages/ 405 2589 0 1.1 Microsoft Office Protocol Discovery - - -

I have not yet been able to determine how I can stop this error.