Showstopper: Problem with EWS requests to Office365 Public Folders

Hi guys,

approximately 2 days ago our customers clashed with 2 problems during access to Office 365 Public Folders via EWS API.
One of problem is described here
https://github.com/OfficeDev/ews-managed-api/issues/263
when enumerating public folders:
****An internal server error occurred. The operation failed., Unable to cast object of type 'Microsoft.Exchange.Data.Storage.PublicFolderSession' to type 'Microsoft.Exchange.Data.Storage.IMailboxSession'.****

Can someone explain what does it means? And why it happened now - because earlier all worked correctly.

2nd problem with EWS PullSubscriptionRequest on Office 365 Public Folder.
More exactly problem happens on the next call of GetEvents - it returns ErrorNoRespondingCASInDestinationSite.

Earlier all worked perfectly and this happened 2 days ago. I started researching and found such info
https://video2.skills-academy.com/en-us/exchange/client-developer/exchange-web-services/how-to-maintain-affinity-between-group-of-subscriptions-and-mailbox-server?redirectedfrom=MSDN

They describe that for notification subscriptions it's necessary to use HTTP headers
X-AnchorMailbox, X-PreferServerAffinity and X-BackEndOverrideCookie.

But we already use X-AnchorMailbox - we use it along with <ExchangeImpersonation> node and set it in the same value - <PrimarySmtpAddress>.
But PrimarySmtpAddress for ExchangeImpersonation it's always user-mailbox address, not PublicFolder.
Then I also found such info
https://video2.skills-academy.com/en-us/exchange/client-developer/exchange-web-services/how-to-route-public-folder-hierarchy-requests

So I tried to use as X-AnchorMailbox in GetEvents request the value from Autodiscover response in node
Account/PublicFolderInformation/SmtpAddress - this value looks like AllPublicFolders?Office365?_fdbae65d@...
After this the error ErrorNoRespondingCASInDestinationSite disappeared BUT no any notifications are returned.
I use only X-AnchorMailbox -> so I wanted to try also X-PreferServerAffinity and X-BackEndOverrideCookie as they describe BUT <PullSubscriptionRequest> does not return any X-BackEndOverrideCookie.

So I have several questions on this 2nd problem:

1. Do I understand correct that ErrorNoRespondingCASInDestinationSite started hapenning 2 days ago because CAS server for user-mailbox (which account we use to connect to Office 365) was changed and now is not the same as for PublicFolder ?
2. How correctly to form EWS requests to Public Folders
   a) Is ExchangeImpersonation necessary? If yes - what address to use (we use SMTP-addr of user who connects to Office 365) ?
   b) what address to use in X-AnchorMailbox ?
   c) is X-AnchorMailbox enough (because X-BackEndOverrideCookie is not returned by PullSubscriptionRequest)
   d) if I use these 2 EWS requests correctly - PullSubscriptionRequest and GetEvents - i.e. use
   ExchangeImpersonation/ConnectingSID/PrimarySmtpAddress = admin365@...
   and
   X-AnchorMailbox = AllPublicFolders?Office365?_fdbae65d@...
   WHY I stopped to get any notifications

Any help highly appreciated.