openRecord not opening record

I have a database, written many years ago, which I use on macOS and iOS. It contains a table called Start, whose form is designed as a switchboard for database navigation. In the database Options I have a 'Trigger after open' of openRecord(record(Start,1)), which brings up the form on opening the database. This has worked perfectly for many years until the latest version of Ninox (3.13.3), where the form starts to appear and then immediately disappears again, leaving the record selected but no form visible (i.e. openRecord is selecting the record but not opening it). If I manually select the record, the form appears as normal. I have checked the documentation and the syntax still appears to be valid. So could somebody please tell me if this is a bug in the latest version or has something changed in the way openRecord works of which I am unaware? Many thanks for any help you can give.