Sharepoint Online remote event receivers attached with Add-PnPEventReceiver depend on used authentication method

Today I have faced with another strange problem related with SPO remote event receivers (wrote about another strange problem here: Strange problem with remote event receivers not firing in Sharepoint Online sites which urls/titles ends with digits). I attach remote event receiver using Add-PnPEventReceiver cmdlet like that:

Connect-PnPOnline -Url ...
$list = Get-PnPList "MyList"
Add-PnPEventReceiver -List $list.Id -Name TestEventReceiver -Url ... -EventReceiverType ItemUpdated -Synchronization Synchronous

In most cases RER is attached without any errors. But the question will it be fired after that. As it turned out it depends how exactly you connect to the parent SPO site with Connect-PnPOnline: remote event receiver is attached successfully in all cases (you may see them in SPO client browser) but in some cases they won't be triggered. In fact I found that they are triggered only if you connect with "UseWebLogin" parameter, while in all other cases they are not. In the below table I summarized all methods which I tried:

#	Method	Is RER fired?
1	Connect-PnPOnline -Url ... -ClientId {clientId}-Interactive	No
2	Connect-PnPOnline -Url ... -ClientId {clientId}	No
3	Connect-PnPOnline -Url ...	No
4	Connect-PnPOnline -Url ... -UseWebLogin	Yes

Strange problem with remote event receivers not firing in Sharepoint Online sites which urls/titles ends with digits

Some time ago I wrote about Sharepoint Online remote event receivers (RERs) and how to use Azure functions with them: Use Azure function as remote event receiver for Sharepoint Online list and debug it locally with ngrok. When I tested RERs on another SPO sites I've faced with very strange problem: on those sites which urls/titles end with digits remote event receivers were not fired. E.g. I often create modern Team/Communication sites with datetime stamp at the end:

https://{tenant}.sharepoint.com/sites/{Prefix}{yyyyMMddHHmm}
e.g.
https://{tenant}.sharepoint.com/sites/Test202111221800

I noticed that on such sites RER was not called because of some reason. I've used the same PowerShell script for attaching RER to SPO site as described in above article and the same Azure function app running locally with the same ports and ngrok tunneling.

After I created site without digits at the end (https://{tenant}.sharepoint.com/sites/test) - RER started to work (without restarting AF or ngrok - i.e. I used the same running instances of AF/ngrok for all tests which ran all the time). Didn't find any explanation of this problem so far. If you faced with this issue and know the reason please share it.