Per feedback from @Sneha, a designer who uses the feature regularly:

• On the phone I cannot scroll up to Alt text input field once keyboard is up Fix in progress - T386834
• When I am writing a caption I often leave the app to look for more information in order to compose a caption. Every time I leave the app the caption I wrote disappears and I have to re-write it again. Also when that happens the caption help text needs to be manually erased. - filed new bug task: T388933
• On the preview page the photo appears at the bottom of the article which seems to give a wrong impression on where it would appear eventually (as it actually goes on top of the article if I am not mistaken.) - filed with this task T363947
• On the preview screen the caption is not clearly visible in dark mode - commented on: T374910
• Sometimes caption preview is not visible at all if I leave the app and come back and edit - related to T374910
• After I publish it goes directly to the next suggestion but it would be nice to actually see how it appears on the page for confirmation. (Noted on T364157)
• On article pages the main image caption is not visible so as an editor you would not see the importance of adding a caption. (Noted, it's visible for where the image is actually inserted, but not for the re-used header image)