Not normal, unfortunately. On any Yamaha you should be able to leave the USB in and not have to keep unplugging and plugging back in.
Keep in mind certain models have a lower power draw available for the USB port (the PSRsx600/DGX670 for example) so you will have trouble getting anything larger than a 32gb to register (some very energy efficient 64gb sticks will work, but that's blind luck).
There are apps you can use to measure the mA (current in milliamps) draw of each USB device. I suspect the USB stick you're using has just a slightly high power draw; Find a lower power draw one (usually smaller size, but also slower) and see if you can successfully leave it in on bootup
Most ports can provide:
USB 1.0, USB 1.1, and USB 2.0 standard downstream ports can supply up to 500 mA (milliamperes).
USB 3.0 standard downstream ports can provide up to 900 mA.
USB 3.0 charging downstream ports can supply up to 1,500 mA.
I found out empirically that 700ma was the max current draw back in the Tyros 2 era, but as I no longer have easy access to a bunch of USB powered hard drives (if you look underneath it tells you the current draw of each one individually. Even the same model doesn't guarantee a current draw) so I don't know what the current draw of the PSRs770 is.
But in a nutshell, see if you can find a smaller USB stick and try that (I have a 128GB main stick which doesn't work on DGX670 or PSRsx600; probably too much current draw for them to handle. I initially thought it was a FAT issue (PSR3000 and CVP300 series are only Fat 16 right out of the box, so you can't use a USB stick larger than 2GB on them) but then someone else on this forum said they got a 64gb stick to work on a DGX670/PSRsx600, which suggests current draw as the limiting factor.
Cheers,
Mark