Sonarr version: 3.0.3.644
Mono version: 6.4.0.198
OS: Lubuntu 18.04.3 LTS
Debug logs: https://file.io/cb5CNr
Description of issue:
In Firefox 69.0.1 (64-bit) (inc. Safe Mode) –
I’m seeing excessive CPU use (~80%-95% on a single core AMD) when idling on Calendar page in Month | Week | Forecast | Day views.
Clues:
It does not use excessive CPU on Agenda view.
It does not do it on:
- Series | Add New | Import | Mass Editor | Season Pass
- Activity | Queue | History | Blacklist
- Wanted | Missing | Cutoff Unmet
- Settings | Media Mgmt | Profiles | Quality | Indexers | D/L Clients | Connect | Metadata | Tags | General | UI
- System | Status | Tasks | Backup | Updates | Events | Log Files
It does not do it if I move off the Firefox tab containing Sonarr and view some other tab. It does it only when Sonarr is in the active (focused) tab and only when viewing the Calendar page (in one of the above mentioned views).
It does not do it if Firefox is minimized and not actively drawing the Sonarr Calendar screen. Yet it does do it if I Alt-tab to another program and Firefox is merely hidden in the background. It does not matter if the other app is full-screened or windowed.
I hope that’s enough info for a light bulb to go off.
I am available if you need a guinea pig. Just lemming know. 
Note: while generating the sonarr.debug.txt I periodically switched from Calendar to System and back to Calendar again to see if it might trigger some enlightening behavior to be captured in the log file. This is noted in the log by System’s Health, Status and Disk Space check entries.