ChatGPT won’t open/analyze Excel/CSV files

I’m trying to run some basic statistical analysis (SDs, gain scores, ANOVA) on a small dataset in ChatGPT Plus (GPT-5.1). I try to upload my Excel sheet dataset for analysis, but the model can’t seem to open or read the spreadsheet. It recognizes the file but throws an internal error when trying to load it??

Is this a known issue right now?
Has anyone found a temporary workaround to make ChatGPT read data files again? Is there a different feature or GPT that people use?

Thanks in advance for any solutions. This has been an annoying roadblock for me.