quota:
check the package, try to edit or make new package
502 bad gateway:
change the webserver to apache
restart service, if you want to. you can reboot your vps
btw how much you SSD/HDD IO Speed ?
how to check ?
go to your "free" folder like /usr/local/src
then type
dd if=/dev/zero of=test bs=64k count=16k conv=fdatasync
see the result
after that try to delete test file:
ls -al
see the file test? delete it