I’ve had the same issue, too, only on my 13-inch 2016 MPB - a 63k / 600 line TaskPaper file occasionally pins the CPU at 100% for a couple of seconds. I haven’t noticed it at all on my 2010 iMac.
It also seems to be totally inconsistent. (Just opened the file on the MPB and it’s working just fine today…)
Ok - I was just able to trigger the high CPU load by moving the TaskPaper window onto my second monitor (an iPad running Duet), with TP in full-screen mode.
Dragged it back onto the 1st monitor (i.e. the laptop screen) and it pegged at 100% / not responding for a bit. Then working normally.
Then putting it into full screen on the laptop monitor pegs it again briefly.
Unplugging the iPad (i.e. switching back to a single monitor config) also pulls TP CPU usage up to 100% but very briefly.
I moved a bunch (maybe 100 lines) of @done tasks into a separate file yesterday to try to fix this but it’s still here.
Hopefully this is helpful – it’s not a huge problem, and the approach of narrowing the view to a specific project as suggested definitely cuts down on the CPU usage.