You can try creating file /storage/.kodi/userdata/autoexec.py and if doesn’t work try changing first sleep time.
import xbmc
import time
time.sleep(10)
# disable and enable addon
jsonCmd = '{"jsonrpc":"2.0","id":1,"method":"Addons.SetAddonEnabled","params":{"addonid":"pvr.hts","enabled":false}}'
jsonRv = xbmc.executeJSONRPC(jsonCmd)
time.sleep(1)
jsonCmd = '{"jsonrpc":"2.0","id":1,"method":"Addons.SetAddonEnabled","params":{"addonid":"pvr.hts","enabled":true}}'
jsonRv = xbmc.executeJSONRPC(jsonCmd)
You could delay starting kodi until USB disk is mounted with some loop in autostart.sh file. Then pvr client doesn’t need to be restarted.