I've been wrestling with approximately this problem for a while. (Dorico Pro 5)

I imported some music XML with 1.5 beats in a pickup measure. Everything is fine as far as engraving the music, but if I "play" the tune, the first measure is played with the end of the measure full of rests. I could not get the above steps to work. They insisted on pushing the following notes forward by 2.5 beats by inserting rests at the beginning of the second measure.

I made it work by switching the first measure to 3/8 before changing it to 4/4,1.5. Evidently, changing to 3/8 made something that works like invisible rests in the first measure go away.