Visual showing nothing when no changes to underlying data were made

it would really depend on where the data is coming from i guesss, what source are you using to pull this data? 

There could be a myriad of reasons to be honest but its hard to know without being able to look.

This does happen with data, the easiest solution very often is just to from the text data, create a new date column using a transformation  to force the date format you want, so if you are able to share the date values as I am sure those aren't private I  can show you how to force the format you want in power query, this is sometimes easier than trying to control a unpredictable source, however if you can figure out why it is happening, or if you provide the data with only the dates in it that would be useful.