2. charge move TM

Just tried on Charizard, Venusaur and Meganium and couldn't get a different type of charge move on any (dragon claw/sludge bomb/earthquake).

Is its first charge move Dragon Claw? The second charge move cannot be the same as the first.

If its first charge move is Blast Burn, then either RNG hates you or a bug.

Had it once with Blissey

I was able to get Focus Blast on my Shadow Ball Mewtwo after three CTMs. Ice Beam --> Flamethrower --> Focus Blast

Try waiting until tomorrow. Sometimes that seems to help, but the evidence that it does is anecdotal - people blowing 10-30 CTMs to get one move and not getting it, then getting it with the first CTM the next day.

I'd guess bad RNG. Personally I'm waiting a little bit before blowing dust on TMs to get 2nd charge moves. The only 2nd move I've unlocked so far is on my maxed SB Mewtwo who luckily rolled Focus Blast right away.