Xamarin.Forms 2.3.4.224 iOS crashing on ObservableCollection changed

Tried updating to the new version on iOS but it is crashing on an ObservableCollection binded to a ListView . The errors is:

0x00000001000f41a8 0x00000001000dc2a4 0x000000010041eaf8 0x0000000100367094 0x0000000100d344fc 0x0000000100d32ef8 0x0000000100bc82a8 0x0000000100bca834 0x0000000100bc98c8 0x0000000100bf4fa8 0x0000000100bf5cb0 0x0000000100bf4f48 0x0000000100bf5aa4 0x000000
*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Invalid update: invalid number of rows in section 0. The number of rows contained in an existing section after the update (1) must be equal to the number of rows contained in that section before the update (1), plus or minus the number of rows inserted or deleted from that section (1 inserted, 0 deleted) and plus or minus the number of rows moved into or out of that section (0 moved in, 0 moved out).'

Returned to 2.3.3.193.

Any idea what is wrong?

Thanks,
Dan