When using an OAI set with a mapping to a repeatable field, only the first occurrence of the field will be taken into account. The mapping need to look at all occurences to avoid records missing from the OAI set.
It looks like it was fixed in 20.05 by bug 24531 and I cannot reproduce the bug on master. Can you provide a test plan please ?
Hi Julian, sorry for causing you extra work and thank you for looking into this! We just verified today that it works correctly in our 20.11 installation, but I didn't get to update the bug yet. But also glad to see our tests verified by a bug fix - I couldn't locate it before I filed this. *** This bug has been marked as a duplicate of bug 24531 ***