Update:

I replaced a couple of the small-value electrolytic capacitors around the frame output IC Q301 (TA8427K):

C320 (100µF)
C305 (1µF)

I also re-made some of the solder joints in that area.

The TV worked OK for a day with the white horizontal line still bouncing at the bottom of the screen. However, it has the frame-collapse problem again. Tapping the TV recovers it!

I will try re-soldering the frame output IC and coil connections.