Image alt text intermittently not read in courses created before 2024

I have a set of courses that I created between 2019-2022. The images in the courses have alt text written for them, and when we tested the courses in Review 360, the alt text was read by screen readers (SRs).

Now, in 2024, we're updating the courses and retesting them, but the alt text is only being read by SRs intermittently. For example, the SR may read the alt text of images in 2 out of 5 lessons or not read any alt text in any lesson in one course but read it fine in another course created the same way.

If I copy the existing alt text to notepad and paste it back, the SR can sometimes read the added alt text. If I delete the existing alt text and type it in by scratch, the SR can sometimes read it. But nothing is working to 1) read the existing text that SRs could read before 2024 or consistently read new alt text.

Has anyone else faced this issue? Any solution suggestions? TIA