Compose key with punctuation shows Unicode "composition symbol"

I’ve been using .XCompose files for a while with ibus for input and it has been working fine. <Multi_Key> <period> <period> gives me …

Recently, though, I’ve started getting a weird symbol when I do <Multi_Key> <period> (i.e. before I finish the key)

Normally, I couldn’t select it because it was a transient symbol and disappeared as soon as I cancelled the compose (and clicking the mouse cancelled it). But one time I broke the compose flow and managed to catch it: ⎄. (U+2384 “COMPOSITION SYMBOL” followed by the fullstop in this case)

Is there any way to stop this character showing? Or is it because the punctuation overlaps with some accented characters (e.g. Ṗ) and it’s the new way of showing it? (Previously I think it showed the output for the shortest match but kept it underlined if there was also a longer match)

System: Tumbleweed 20181022, Gnome 3.30, ibus 1.5.19, LC_ALL=en_GB.UTF-8