If saving a string that contains %20 in a text field, it strips them out. Doesn't convert them to a space - they are just gone. If I set field type to url it doesn't strip out the %20, but I have some cases where I have that in a field without it being a complete url. This is when saving posts in WP admin.
Same results on multiple sites. Tested deactivating all other plugins and only running MB 5.6.18 and MB AIO 1.20.0, but no change.
Interestingly if I add/update a post via wp_insert_post() there is no problem with it saving %20. It's only when saving through standard WP editor that it strips them out.