Hi Dan,
I had a look at this problem, using the APP on iOS (iPad). There I found that the ?Split¡° option doesn¡®t appear in the Hamburger menu if you select the lead message (normally the oldest one of a topic) - it is only visible in the subsequent messages. Which makes sense of course, as the oldest message defines the topic.?
How this works if the Topic has been created by manually merging multiple messages I don¡®t know, I¡®ve never done that. I can only suspect that you¡®re trying to split the message from the topic that GIO takes as the lead message already.
Kind regards
Thomas
Thomas Gruber