I have the same issue (which I think is the same as Aleh describes below).
I have an hybrid Exchange setup with on-prem Distribution List, with 35 users and 1 MEPF. For on-prem users this works fine. For users with mailboxes in Office 365, when they email the DL, the email is received by all 35 people but never to the MEPF. The sender never gets an NDR either.
I have the latest version of AAD Connect, I ticked the box to enable sync'ing Exchange Mail Public Folders, and confirmed I have Microsoft Exchange System Objects ticked in 'Domain/OU Filtering' section. After running a sync, I can see in Synchronization Service Manager that all my MEPF's have sync'd sucessfully (no apparent errors).
However, when I try to send an email from an O365 mailbox user to the DL, it doesn't arrive - no NDR also.
Is there somewhere in O365 Admin Centre to view the MEPF's? There is a tab for Users (Active Users, Contacts, Guests) and Groups (Groups and Shared Mailboxes) but nowhere to see smtp addresses for MEPF's.
If I expand the DL in Admin Center, I don't see the MEPF either.
Emailing the MEPF smtp address directly from an O365 mailbox works fine.