Such problems are addressed by quite a number of students. Now the issue which yields lower percentiles with considerably good marks is the normalization. So if the paper of the shift is easier than the others then its expected that you will get a considerably less percentile despite of having good marks. This are the procedure of normalization and the decision of hard or easier is entirely depend on the definition of NTA.

So this is a reason behind this fluctuations. I would recommend you to attempt the further session of JEE MAINS.

I hope this might help. All the very best for your future endeavors!