I'm using version 21.0.7. In my project, I have a series of bubbles containing text that float to the top of the stage. When I export and watch the video, the text within these bubbles is jittery, i.e., the letters shift from left to right. Each bubble is a graphic, made from an .svg file I imported to the library from Illustrator, then classic tweened along a guide path. I tried making the bubbles with motion tweens, but I can't get the hang of making the motion path exactly how I want it, with just the right curves. The method I described above has served me well, save for the jittery text. You might ask why I didn't just make the bubbles themselves using the illustration tools in Animate, and it's because I think they're awful compared to those in Illustrator. The larger bubble graphic shown below, I made in the same way, and the text doesn't shift on these, only the smaller ones. I went ahead and made another small message bubble graphic using the tools in Animate, and no, the text doesn't shift on this one. But still, why does this text shift on the small bubbles made in Illustrator and not on the big bubbles? I'd still prefer to design these elements in Illustrator, because that's what the program's made for.
tweening text is tricky. it's easier to break text apart (usually twice) to convert to a shape and then group those that you want to group (ie, they're not converted back to text) and then tween the shape.