Besides of Gary's suggestion, and If I don't remember it totally wrong, there was a video at web about some weak soldering issues about lamps / buttons.
But, I don't think it was as many as you mention, and not too sure if it was T4 or T5.
If I find the video (most likely at YT), I'll post the link.
Edit:
Found this, and I think it was the T5 I had in mind....
Hope it's for any help.
Video about open / tear down a T4, and soldering bad lamp connection inside T5.
https://www.youtube.com/watch?v=iaxE4i9x_S4https://www.youtube.com/watch?v=hJPl_Kp06AY&t=88s 
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