What would cause a circuit to become hot when a breaker is turned off?
The circuits are “crossed” at one, or possibly more, points. Be very careful when sorting this out.

This is how people get killed by electricity as they think they have isolated something but it is still live.

The method to find it is to disconnect at each junction until the relevant part goes dead and label wires to work out what goes where.

Had a similar problem where a site had been wired with additions over 30 years and most was not labelled... the law changed and it all had to be identified. Relatively easy as it was between buildings, switch of a breaker and 15 seconds later the phone went : “we have no power.. oh, where are you?” That was that breaker labelled... Good fun, but we did not mention those power cuts were deliberate... :)