It seems like zooming in and out of the webpage effects a lot of the gameplay. I had terrible luck with the miners when my zoom was set to 100%. They wouldn't climb back up to chop another block after they finished the first one, but it looked like they were programmed to do so.
And when I upgraded their speed (I think lvl 6 with the red boots) they became so fast they could not center on a block to break it rendering them completely useless.
Also I could not figure out what the secret Click Radius power up was or how to unlock it.
Zooming out on the webpage itself seemed to be the answer. I set zoom to 25% so the game was ridiculously tiny and the miners were able to dig again and they could climb back up to break multiple blocks after finishing their first one. I think even setting zoom to 75% is enough to get these features to function as intended.
And hovering over the center of the spire (at 25%) allowed my power click to reach nearly every block in the layer without moving.
Anyway, was finally able to max out every upgrade after that. Fun game. For me the bugs were simultaneously obnoxious and a fun mystery to solve.
I'm on a Windows computer with a Chrome browser.