TM charge bug
Is it just me or TM charging moves is getting more consuming.
It took me 14 TMs to change charge move of 3 pokemons into ice moves.
I asked others too to change charge move of a Piloswine. It took him 8 TMs still alternating between Bulldoze and Stone Edge.
Answers
My rule of thumb is one try, and wait until tomorrow. From anecdotal reports, there's something in the code (maybe a bug, maybe deliberate) that tends to take you back to what you had if you CTM it again very soon. So, Walrein, has Earthquake, and you CTM and get Water Pulse. Wait until tomorrow to try again. The CTM and the Walrein will still be there.
RNG.
I've used 10 CTM's on 4 different Machamps, trying to get Close Combat or Heavy Slam to change to Dynamic Punch. EVERY time I use one, CC becomes HS or HS becomes CC. EVERY SINGLE TIME. I have not changed one Machamp's Charged Move to Dynamic Punch.
I've used 2 CTM's on Hariyama's to change Heavy Slam to Dynamic Punch. Both times I got Dynamic Punch.
RNG, man - I'm not sure if Niantic uses the same definition of "Random" that I do.
