Error connecting a file

Hello all,

I've loaded up my Power BI file after the weekend, and now cannot 'refresh' the data without a couple of errors occuring. After playing about with the model - the issue is caused by connecting a folder containing excel (CSV) files - and error codes also show when trying to connect a new folder. The folder connection worked fine prior to the april update, and the error codes are:

"object reference not set to an instance of an object"

"A Task's exception(s) were not observed either by Waiting on the Task or accessing its Exception property. As a result, the unobserved exception was rethrown by the finalizer thread"

EDIT: Found the excel file causing the issue, but no clue what the issue really means since it all worked fine previously? Is it a case of checking all the formats for each column? The only issue is the file has 1000+ columns🙃

Anyone got any thoughts on a cause/resolution please?

Many Thanks!