Received the following from a query to /rest/api/3/Search
{“errorMessages”:[“Date value ‘2021/03/28 01:09’ for field ‘updated’ is invalid. Valid formats include: ‘yyyy/MM/dd HH:mm’, ‘yyyy-MM-dd HH:mm’, ‘yyyy/MM/dd’, ‘yyyy-MM-dd’, or a period format e.g. ‘-5d’, ‘4w 2d’.”],“warningMessages”:}
2021/03/28 01:09 seems compatible with yyyy/MM/dd HH:mm
Started happening on 3/27 at 6PM PDT (3/28 1am UTC).