I have a scripture theme having the scripture centred in the centre 1/3rd. Adding scripture is completely random in its autoflow & sizing. If I add 3 or 4 verses it gets smaller adding more scripture words per slide (as it should), using CTRL select, until if gets to verse 5 & it jumps back to bigger font sizing with less words. After that it seems to keep them in the incorrect larger font, but if you remove a random verse it jumps back to the correct smaller font size with more words. This used to work fine & not sure if it just doesn't like the theme.

Please make sure you've updated to 6.7.9.1 and also check the minimum font size in options.