In a battle between an Armaldo and a Mega Medicham, Armaldo was able to outspeed the Medicham, and use Knock Off. With the speed stat of Armaldo, this is not possible. I'll explain more in detail but first here's an import to the two Pokémon used.

Armaldo (M) @ Leftovers
Ability: Battle Armor
Happiness: 225
EVs: 252 HP / 92 Atk / 166 Spe
Adamant Nature
IVs: 14 SpA
- Smack Down
- X-Scissor
- Knock Off
- Brick Break

Medicham-Mega (F) @ Medichamite
Ability: Pure Power
Level: 53
Shiny: Yes
Happiness: 205
EVs: 252 Atk / 6 Def / 252 Spe
Adamant Nature
IVs: 2 SpA
- Fake Out
- Ice Punch
- Zen Headbutt
- High Jump Kick

(Armaldo was Ordinary in Size, in a Regular PokéBall. Medicham was Ginormous in size, in an Ultra Ball)

I'll also explain turn by turn how it went:

Turn 1: Medicham Mega Evolves, uses Fake Out. Armaldo Flinches
Turn 2: Mega Medicham uses High Jump Kick, but Armaldo was able to move first and use Knock Off.

(Tailwind or other stat modifiers were not applied. Also, note that we had Raise to Cap turned on, and the Medicham was leveled up to 100 due to that so they both are supposed to be at level 100)

Because they both are at level 100, it is impossible for Armaldo to outspeed Mega Medicham as there is a 132 stat point difference in their speed. (Used Pokemon Showdown to calculate)

When I was testing, I did say Raise to Cap was turned on and Medicham was at level 53 at the time, however, I leveled it up to 100 and this happened:

Turn 1: Medicham Mega Evolves and uses Fake Out, Armaldo Flinches
Turn 2: Mega Medicham outspeeds this time, uses High Jump Kick, knocks out Armaldo.

This leads me to believe that Armaldo outspeeding was caused due to the Raise to Cap being turned on and Medicham being leveled up to 100, and the stats of the Mega Medicham not updating accordingly based on that. If you go on showdown and you check the final speed stat of a Mega Medicham, same stats as shown above, it shows that Mega Medichams speed would be 160. Armaldo is 167.

tl;dr: When using raise to cap to level up pokemon to 100, its speed stat didn't update as it should have. a pokemon that should have had 299 speed had 160 speed.

" If you go on showdown and you check the final speed stat of a Mega Medicham, same stats as shown above, it shows that Mega Medichams speed would be 160. Armaldo is 167. "

I had meant to say " If you go on showdown and you check the final speed stat of a Mega Medicham thats level 53, same stats as shown above, it shows that Mega Medichams speed would be 160. Armaldo is 167. "

Thanks for the detailed report. We were already aware of some issues regarding stats with mega evolutions and raise to level, but this adds some extra detail and information so I have put this on to the internal ticket we have. I was able to confirm all that you said, and also that at level 56 the Medicham outsped the Armaldo, which is consistent with it having its level 56 speed, so it looks like the stat is just lowered to that level.