I have 8 of these cameras, all purchased and set up about 1.5-2 months ago.   I have them all recording to sd, and also using my synology nas / surveillance station to record/stream them via RTSP (tcp).   

Before the 1.3.1 firmware, they were working perfectly.  Nice, smooth real-time views, however, after the 1.3.1 update they are showing a frame every 2-4 seconds, and randomly lagging behind for hours.

Changing hardware acceleration did not help with the quality.

Within synology ss, it 'found' them with onvif and I do have them set up as Tapo c120 cameras in there.  I've also removed, then tried adding as generic onvif.

The c110s and c210s I have are still running smoothly in synology ss in 'live-view'.

Viewing the c120s from the tapo app in live-view seems fine. For me, it's something with the RTSP.

I've seen others (on reddit) with similar issues when trying to view with RTSP.