I’m sorry for this unexpected change in behaviour. It’s caused by the changes we have made in Dorico 5.1.10 and 5.1.20 for the handling of playing techniques that need to go either side of holds and pauses. Dorico now effectively has three “lanes” for playing techniques: glyph-based playing techniques that go inside holds and pauses; text-based or grouped playing techniques that go outside holds and pauses; and bowing marks, that go in their own layer. The order of the latter two layers can be swapped if need be, by way of an engraving option on the Playing Techniques page.
The Tucking index property now works only when you have multiple playing techniques within the same “lane”, though it’s hard to intuit this from the way things are presented in the Properties panel, of course.
I think your proposed workaround of grouping the 1x playing techniques with no continuation line is the best way forwards, because that puts both the 1x and A1/A2 playing techniques in the same “lane” and hence allows you to tuck them as you require.