Current monitor circuit not working
When I see a "high side current sensing" circuit like this, I always first check that the opamp can handle the input voltages. It needs to compare a small voltage very close to the positive supply rail so the "input voltage range" needs to support that.

Your OPA4251 has an input voltage range of:



So it can support input voltages up to V+ -0.8 V. In your PCB schematic that V=V+ = 2.5 V, that means the inputs of the opamp will work up to 2.5 V - 0.8 V = 1.7 V. You're using them close to 2.5 V and that's outside that range!

You can either power the opamps with a higher supply voltage (like 5 V, this is what you did in the first schematics but not in your PCB schematics!)

Or use an opamp which can support input voltages up to it's own positive supply rail. Some opamps with a rail-to-rail input support this.

Do note that in your original schematic you fed the opamps with + 5 V which is enough to drive the N-channel MOSFET. At the 2.5 V you're using in the PCB schematic, this might not be enough.

I would suggest: feed the opamps with +5 V (instead of +2.5 V) like you did in your first schematics.