Hi @tiny-universe!
First up, yes you can delete imported GPX data. in the “…” menu on the Item Edit view for any items imported from GPX you should see an option, “Delete imported GPX data”.
Though I’m not certain that the weirdness you’re experiencing will be related to the imported GPX data. I suspect it’s merely coincidental. If Arc is having ongoing slowness or other weirdness it indicates an ongoing problem. One patch of bad data will typically only cause problems when viewing the timeline for that particular day or date range.
So it sounds like something else is causing problems on an ongoing basis. What you describe actually sounds quite similar to a problem someone else reported yesterday: Many problems since the last update - #5 by matt
In that case it was likely due to Arc Mini having communication fails with Arc Timeline and causing conflicting recorded data problems. If you do have Arc Mini installed, I recommend uninstalling it, and switching to using Arc Recorder as a backup recorder instead. Arc Timeline and Arc Recorder work really well together, while Arc Mini is … well, it’s past its use-by, and will be removed from the App Store soon.
If you haven’t been running Arc Mini then I don’t have a good explanation for the weirdness! It shows all the usual signs of there being weird/nonsense timeline data that’s clogging up the processing engine and causing it to churn away, trying to process the timeline but failing, which results in it taking up way too much time and CPU while also still failing to do a good job. And currently the only cause for that that I’m aware of is if any of the Arc family of apps is having a communication breakdown and trying to record at the same time as one of the others. Arc Timeline and Arc Recorder communicate really well, but Arc Mini is currently the problem child, making it the most likely cause.
If you don’t have Arc Mini installed, then I’ll have to put on my detective hat and start digging deeper, which might require sending you a debug build so we can get some detailed logging and more clues.