Huge problem with iCloud Photo Sharing

Dear all,

I am writing this here to make this issue public and to have some feedback from some of the great experts here.

What I am about to report is already being treated as a highest priority issue from a Specialist at AppleCare who has put my practice into Escalation mode in order for it to be taken care of by Cupertino's engineers.

In short: since a few days iCloud Photo Sharing is not working.

My current hardware/software situation is:

- MacBook Pro (2016, 15" - macOS 10.13.3 -> iCloud Photo Library & Sharing both active)

- iPhone 6s Plus (iOS 11.2.6 -> iCloud Photo Library and Sharing both active). VERY IMPORTANT (it seems): iPhone space optimisation is active and all of my pictures (since iOS 11 update) are stored in a very small resolution (even if I have 30+GB free on my phone).

- iPad Pro 9.7" (my girlfriend's tablet, whose account is in my Family account and with whom my iCloud Drive subscription -200GB- is shared)

Steps to reproduce:

1. On the iPhone, select a bunch of photos (in my case it was 112 photos and 1 short video), hit the Share button and select iCloud Photo Sharing
2. Create a new album and send them there.

   At this point the phone should be stuck into 'Preparing...' as it is downloading the pictures in high resolution from iCloud (even if I don't know why it cannot just move them from a folder to the newly created one).

Expected results:

The album gets created and you can go on inviting people.

Actual results:

• The album is created but I get an error saying that the iCloud Photo Sharing function could not be used and it asks to try later.

  Interesting: if I select only up to 20 photos (instead of 112 as before) the moving of the pictures succeeds BUT ...

• If I go on my Mac the album is correctly seen but ... there is NO picture inside (please notice that all of those pictures are already in the Photo Library as they were correctly synchronised).
• If I invite my girlfriend to share the Album she NEVER gets the invitation (and, interestingly enough, if she invites me back on another album I never get the invitation).

As of tonight, my Mac now sees 6 pictures instead of 1 (but of course no 112!) and there seems to be another issue with document sharing as activating the collaboration feature on Numbers gets the invitation message to my girlfriend but then she gets an error which says the spreadsheet cannot be retrieved.

I should get an answer from the engineers in a few days but, in the meantime, could you please try to think what all of this could be, if it has ever occurred to you before?

iCloud status says everything is alright but ... should I trust it?

Thank you