Tuning doesn't work even with Gemini Pro 1.0 for datasets containing outputs with more than 5000 characters

From the official website, it mentions the output character limit for training dataset as 5000 only for Gemini Flash 1.5 model. But I am unable to tune even with Gemini Pro 1.0 model. Important to note that I was able to do it a few months back, but it doesn’t work now. It feels like a backward step and I need to get this done asap! Any thoughts on this?