Strange measurements between panel and controller

Is the controler PWM or MPPT.

The controller is MPPT, a cheap one (15 dollars) so I wonder if it is really MPPT

Argh !!

You are crashing your controller. ???

The battery is ALWAYS the first connected and last removed. The PV is last connected, and first removed.

The controller uses battery power to boot up and then it can manage the PV input. If you are installing and removing a series amp meter, you are also removing the battery power from the controllers brains.

No, I am using a fixed amp and volt meter between controller and battery.
I first connected battery to controller and then controller to PV
I just wanted to know the current coming in the controller, so I put my digital multimeter in series with the + wire that goes to the controller and I measured less than 3 amps where my fixed amp meter between controller aand battery is reading 5 amp
I never disconnected any wires between battery and controller.
So why am I not measuring the same amps before and after controller?

Because that is how a MPPT controller works.

For an MPPT controller, power in ~= power out, not counting efficiency losses which can be high for a cheap MPPT CC.
That means that with Vin = 24V and Vout = 12V, Iin will be half as large as Iout.

If the series meter has too large a voltage drop across it (high shunt impedance) then the input voltage at the CC will not be the same as the output voltage of the panels.

Also realize that the output of the CC will not necessarily be the maximum that the panels can produce if the battery is at least partially charged and the CC is not in Bulk mode.
The relationship between Vin/Vout and Iin/Iout through the CC will not necessarily change, but the panels will no longer be operating at their MPP. The voltage will rise from Vmp toward Voc as the current drops below Imp.