There is technically nothing wrong with your waypoint missions.
The on screen signal strength indicator shows an average signal strength.
In both graphs the average signal strength is equal, however in the bottom graph the time the signal is weak/interrupted is too long to successfully complete a waypoint mission.
This results in a Signal Lost error.
Manual flying seems to be less sensitive to signal interruptions.
Repairing the drone to the remote makes no difference, it’s unrelated.
For VSC drones (which yours is) it can also lead to strange behavior of the drone, like wandering & spinning around.
For the most stable signal, the remote and drone have to be in unobstructed line of sight, and the RC has to be pointing towards the drone (consult the user manual of the drone).