Analog Oscilloscope Flickering Signal Problem
Figure 1. Trace breaks at 0.2 divisions and restarts at almost 4.5 divisions.

Figure 2. Trace breaks at 0.2 divisions and restarts at almost  4.25 divisions.
The problem isn't your 'scope - it's the signal. You have jitter of at least 0.2 / 4 = 5%.
You can usually confirm that the 'scope is stable using the 1 kHz test signal present on the front panel of most bench oscilloscopes.