HV 12s ESC. Cutting out on 9s

[Jahay]

Hi guys.

I took the truck out for a first run in a year.

Everything was running very well on 6s...no electrical issues.

My truck is very undergeared at the moment. It's geared for 45mph on 6s. The motor was running hot, but the esc was ice cold.

I am running an 11t pinion, and will be going up to a 14t for a theoretical top speed of 58mph on 6s.

Anyway.
As I ran it on 9s, the esc began to cut out every time I accelerated and the esc kept on beeping. I have not experienced this before... And I am unsure whats up?

After this happend, I put 6s back on, and it ran absolutely fine... So it was only acting strange on 9s, and it never had any issues before.

Please advise what the possible issues could be.

The reason I am so undergeared, is because I jphave just remove my baja bow ties and fine back to 3.2 badlands. S considerably smaller and lighter tire.