I have a QU 16 and I use the same Sandisk Extreme thumb drive to record my band’s two to two and one half hour practice every week. I have never had any problems with the recordings. Always finishes the recording with 0 errors. I only use 10 channels and my individual track wav files are usually somewhere between 1 and 1.5 Gb in size, depending on when I start the recorder and how long we go.
I know this does not provide any recommendations for you, but I thought it might be helpful to know that this should work. I agree with your suggestion to try a different thumb drive, but the Sandisk Extreme is usually very reliable and compatible with the QU mixers. They can however be pretty temperamental with USB storage devices.
Good luck!