I can't say for sure, nor how to diagnose this reliably, but my intuition is that there could be some memory leak?
It's not as snappy as I remember.
I do leave the app open, since I switch to/from it often, and when it gets slow a restart (i.e. swipe it up to close from the overview) does help.
Navigating the calendar, interacting with running records under the "timers" tab, all are much faster. Instantaneous vs. handful to dozen seconds of freezes.
How can I narrow this down?