formatting gradually disappears in daily updated workbook

I have a workbook I update from numerous sources every day. A few months ago I noticed some of my formatting started to disappear - a couple of borders were missing. a day or two later a couple of cells which had color were no longer colored. number formatting reverted to general so my percentages just showed up as decimals and my dollar values no longer had a $ or commas. Eventually - over the course of several weeks - all formatting in the document was completely gone. A couple of times throughout this process I tried replacing all the formatting, but as soon as I'd save the file, close it and open it back up whatever formatting related changes I had made would again disappear.

Eventually I went back a couple months and pulled an old file which still had its formatting and updated that instead. This worked fine... for about 2 months. three days ago I started noticing the same issues - a few borders disappeared in the file. two days ago a few more borders were gone and a couple of cells lost their color. yesterday and today it has gradually gotten worse again.

Has anyone else ever seen this happen?

Anyone have any idea what could be causing it / how to avoid?

I cannot upload a sample.

Thanks for the reply Jacc,

I'm the only one who edits this file.

I do the same thing every day - run reports out of an excel add-in called BEx and a web portal called NextGen and paste those into the new workbook.

Only pieces of the newly updated information lose their formatting each day - I would think if there were an issue with the web portal or the add-in the formatting wouldn't survive the initial paste... even if it did somehow carry formatting when i pasted and then lose it when i saved and re-opened wouldn't it drop all formatting in the areas I pasted?

Further, there are sections of the workbook which do not get updated manually which lose their formatting.

Thoughts?

Also, there are three workbooks which get updated with this information.

Only one of them has lost any formatting so far...

i just tried updating the file with paste special / text (the add-in is opened in a separate excel instance) and paste special / formats from an older version of the file which had not yet lost the formatting. most of the cells with values in them that are supposed to have borders now have borders, but no fill survived the save / close, and my date/time fields switched to general formatting.

Also, two of the tables I update have two "Result" rows at the bottom totalling everything in that column. These rows are supposed to be filled with borders and a custom format including $ and , however for whatever reason both rows in both tables did not retain any formatting. most of the rest of the cells in those tables look correct...