The wiring on ST1 while neatly tucked away can be difficult to work on due to that same fact and tight clearances. Had a guy once who had a regular shop repair his back flat and bike would not operate afterward turns out the main leads (large plug three leads) from battery to motor has an intermediate plug under the battery carrier (Stromer uses a different term not at shop now to look it up) anyway they had inadvertently pulled on the plug coming out of the chainstay and disconnected the internal one. Not fun to reconnect. If either of them are loose your readings would be off. Also disconnect and reconnect the other two leads to insure they are making good contact. Remember to remove your main battery before attempting to service any connections to avoid the possibility of arching, surges or other issues. The motor controller is internal to the motor on the ST1 so inspect the wiring exiting the motor to make sure it was not damaged while repairing the flat. Finally check all connections on the display, if you changed the tire with the bike upside down (common on home repairs due to lack of repair stand) the display may have been damaged. When an issue arises suddenly after a repair the cause can usually be traced back to something that was not reassembled correctly, or damaged during the repair. It is always advised to remove the main battery when servicing any of the electrical components even unplugging the wheel to change a flat, maybe I am overly cautious in that respect but have seen too many things happen that the engineers said were designed not to happen. If all your connections are secure even the internal ones and your battery voltage reading (using a voltmeter) is in range to read full on the display. Then I would suspect the display, not overly expensive, easy to replace, cheap to ship and have been known to fail. Anyway that's my two cents worth hope it helps Cpt