Currently using Umami, but I've considered switching to Plausible due to Umami's less-than-stellar development performance (e.g. breaking the site details page for a few days recently).

I switched to Umami for now because the Plausible developers were totally disinterested in fixing bugs that silently dropped data.

These are still JavaScript solutions, so if their JS code is broked then you just don't get the data. You end up with unknown unknowns.

The only truly reliable data you can get is from your server logs, and obviously you are limited by whatever the browser gives you in the request.

Check out Usermaven.com.