On your flash drive, does this file exist? config/plugins/statistics.sender/dismissed? If not, create it. Anything can be in the file
If there is nothing showing on the flash at all, then unfortunately you've been kinda nailed by a design defect in the plugin where *if* the flash drive happens to drop offline (usually caused by using the flash drive in a usb3.0 port instead of 2.0), then the plugin nags and hounds you to install the statistics sender and in effect crashes the entire webUI (Unfortunately, the plugin for some reason does NOT check to see if the flash drive actually exists and is valid before it nags you to install stats). In this case your best is indeed to uninstall the preclear plugin (easiest way would be to delete preclear.plg and statistics.sender.plg from config/plugins on the flash drive via SSH and then reboot.)