It's all downhill from here

I may have (or may not have) solved a mystery involving certain brands of DGT clocks. At Street Chess the DGT Easy and Easy+ models sometimes suffered from a defect where even after pushing the lever, a players time continued to run down. It didn't happen with all the clocks, but it happened often enough so that players simply did not trust them.
What was particularly annoying was that when we tested them elsewhere, they seemed to work fine. Some had been used at other clubs without problem, but at Street Chess they seemed to misbehave. So what was it about Street Chess that was different?
Now it turns out there are a few things that a different (outdoor play, fast time controls etc), but one thing I had not previously considered is that we play on a slope! Not a steep slope. but the tables ar off level by 1 to 3 degrees. And this has me wondering whether the switch mechanisms in the clock do not operate properly under those circumstances. Even after being pressed the lever may tilt back just enough to restart the first players clock, and robbing them of their time. Further investigation is still be done, but if it turns out to be the cause, it will be spirit levels front and centre.