I have  custom object. For this object, there is a Custom Button that calls a flow. This flow is a screen flow that collects information and cretes a record for this custom object, then calls a subflow. It has been working fine for weeks. At ~9:00am ET this morning, the flow was called from the button and performed its function successfully. About an hour and a half later, a user tried to do the same thing. Now, instead they get the salesforce equivalent of the "spinning wheel of death" and the following error message,

"This page has an error. You might just need to refresh it. Action.prototype.finishAction Error [Assertion Failed!: 'descriptor' must be an event or component descriptor such as 'prefix:name' or 'e.prefix:name'. : false Callback failed: serviceComponent://ui.interaction.runtime.components.controllers.FlowRuntimeController/ACTION$runInterview] Failing descriptor: {flowruntime:flowRuntimeV1}".

When I navigate to the flow in Flow Builder and try to use the debug feature, as usual it opens a new tab with the "Dubug Flow" Modal. There are no input variables, so i click "Run". In the main area, I get the "spinning wheel of death" . In the Dubug Details Panel...nothing...nothing at all.

When I check the logs from the Developer Console, there is no error or error message reported.

Does anyone know if there was some change or update for salesforce that might be causing this issue out of nowhere?

Otherwise, can anyone help provide 

I have  custom object. For this object, there is a Custom Button that calls a flow. This flow is a screen flow that collects information and cretes a record for this custom object, then calls a subflow. It has been working fine for weeks. At ~9:00am ET this morning, the flow was called from the button and performed its function successfully. About an hour and a half later, a user tried to do the same thing. Now, instead they get the salesforce equivalent of the "spinning wheel of death" and the following error message,

"This page has an error. You might just need to refresh it. Action.prototype.finishAction Error [Assertion Failed!: 'descriptor' must be an event or component descriptor such as 'prefix:name' or 'e.prefix:name'. : false Callback failed: serviceComponent://ui.interaction.runtime.components.controllers.FlowRuntimeController/ACTION$runInterview] Failing descriptor: {flowruntime:flowRuntimeV1}".

When I navigate to the flow in Flow Builder and try to use the debug feature, as usual it opens a new tab with the "Dubug Flow" Modal. There are no input variables, so i click "Run". In the main area, I get the "spinning wheel of death" . In the Dubug Details Panel...nothing...nothing at all.

When I check the logs from the Developer Console, there is no error or error message reported.

Does anyone know if there was some change or update for salesforce that might be causing this issue out of nowhere?

Otherwise, can anyone help provide 

This is a screen-based flow.
I have the user enter a number 2 times ( to reduce incorrect entries).
Both fields are validated with the following expression (except that the variable is different of course):
REGEX({!scrvar_RCN1},"4[6-9]{1}[0-9]{9}[0-9]{0,1}")
When a valid value is entered, the flow behaves as it should.
When an invalid value is entered ( too few or too many digits or the first two digits do not fall within the specified ranges), instead of getting the supplied error message, the screen collapses to a line and a "spinning wheel of death" occurs that doesn't go away, even after an hour.

When run in debug mode, nothing shows in the log after the previous screen, an assignment component that occurs between the screens and the standard "Transaction Committed - Any records that the flow was ready to create, update, or delete were committed to the database." message that shows up before each new screen.
...so I have no data to troubleshoot further.
I have also tried using the Developer Console, but the only thing that shows is that the user info for the user that pressed Next.

I have tried regex variations of the validation criteria, but all versions show the same pattern(s) of behaviour.

Any insight would be greatly appreciated! Thank you!

Need to allow an unauthenticated guest user to access an inbound flow to facilitate Lightning Scheduler. When navigating to the community page as a guest, I always encounter an error and the flow component does not show. Required objects are granted read only access via sharing rules, as they are not listed on the community's guest profile. Community is build-your-own theme.