Upgraded from v12.5 to v15 – Editing extensions with Polycom SPIP501’s result in Internal Server Err

[la-d-da]

We recently upgraded from v12.5 to v15. After the upgrade, we are unable to edit any extension that has a configured Polycom SPIP501 phone. We get an Internal Server Error(500)
System.InvalidOperationException: Sequence contains no elements
at System.Linq.Enumerable.First[TSource](IEnumerable`1 source)
at ConfigurationManagementModel.CfgStringsEnum.GetValue()
at System.Lazy`1.CreateValue()
at System.Lazy`1.LazyInitValue()
at ManagementConsoleJS.Services.Adapters.CmmAdapter.SerializeCmmEnum(ICfgEnum value)
at ManagementConsoleJS.Services.Adapters.CmmAdapter.SerializeCmmProperty(String wpPropName, ICfgProperty prop)
at ManagementConsoleJS.Services.Adapters.CmmAdapter.SerializeCmmItem(ICfgItem item, Boolean isTopLevel)
at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
at ManagementConsoleJS.Services.Adapters.CmmAdapter.SerializeCmmProperty(String wpPropName, ICfgProperty prop)
at ManagementConsoleJS.Services.Adapters.CmmAdapter.SerializeCmmItem(ICfgItem item, Boolean isTopLevel)
at ManagementConsoleJS.Services.EditorServiceExtensions.ProcessActiveObjectRegistration(IEditorService editorService, ICfgItem obj, PropertyFilter filter)
at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.<InvokeActionFilterAsync>d__28.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.<InvokeAsync>d__18.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.AspNetCore.Builder.RouterMiddleware.<Invoke>d__4.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at ManagementConsoleJS.Middleware.ExceptionWrapperMiddleware.<Invoke>d__3.MoveNext()

We have tried to create new extensions with the Polycom SPIP501 (3.1.x) polycom31x.ph.xml template, but when the phones boot and provision, there is no dialtone or DTMF.
Any help is appreciated.
Regards,
Lauren

 

[la-d-da]

We have over 50 extensions with Polycom SoundPoint IP 501's and several 4000's. Does anyone have these working with v15? They all worked perfectly under v12.5.

Regards,
Lauren