For many years we have made extensive use of JQL to search for specific epics:
"epic link" in ("EPIC-1")especially in Confluence. Articles where such queries already exist are displaying the tickets as expected, but if we attempt to update the epic(s) in a query using the Confluence "Insert JIRA Issue/Filter" dialog, or to run such a query via Jira's advanced search, an error is reported. Confluence doesn't indicate why, but the advanced search says "The option 'EPIC-1' for field 'epic link' does not exist." The epic exists and I can view it.

The non-existent epic message is correct in this case. If the epic did exist, that message does not appear, suggesting that the epic was found despite the "option does not exist" condition.
Our Jira administrator says that Atlassian must have broken this formerly working query and that there's nothing he can do about it. He suggested searching by epic name, but that generates the same error.
The following also fail:
"epic link" = "EPIC-1"
"epic link" != "EPIC-1"
The following succeed, though they're of no use to me:
"epic link" is empty
"epic link" is not empty
Do epic link queries work for anyone else?
Is it possible that there's something about our Jira Cloud configuration that's causing this problem?