it seems that if cards are attached to each other, some resizing might lead to some of the attached cards disappearing. Dettaching other cards and moving them around makes the missing cards appear again. (Browser: Safari)
We have improved something in that area and I cannot reproduce this effect currently. If it still happens, please report back. Ideally with a concrete example (e.g. if you can give us access to a map part where this happenes.)
Thanks for reporting. We have already fixed this and the fix is waiting to be released these days.