48k Sounds like Low pass filter glitch bug please help

Not sure what’s going on here. I’ve been sent some stems at 48k sample rate, I loaded them into a 41K project not realising, standard issue of lower pitch, changed sample rate for the project to 48k and now everything is correct but sounds like a low pass filter is applied, all the top end is removed.

I’ve tried setting the project sample rate before hand and dragging in other audio, same thing happens.

Please help, I only have a few hours turn around on this project.

Thank you

Was something to do with a plugin in control room inserts, even though bypassed, very strange!