Hi,
We’re currently experiencing an issue with ACF Pro v5.7.10.
When using a relationship field type in a repeater, with a large number of pages selected (more than 200 or 300 pages): The save functionality does not work when we attempt to add more pages to *any* relationship field in the same repeater, on the same page.
We can still add pages to relationship fields, however when we click Update: The changes are not saved — The pages we tried to add to the relationship field disappear.
The most common reason that values to not update is the max_input_vars PHP setting https://www.advancedcustomfields.com/resources/limit-number-fields/