Disarming immediately after arming (motors do not spin)

I have recently updated 4.0 to 4.3.6 (fmu2) and have 2 problems that I have had no luck in resolving after 2 days of effort.

1 When I get the all clear to arm on MP in the main screen and the messages window, with the green light flashing, I arm using the zero throttle/right yaw on the radio and the solid green shows. But within 1 second, the fc disarms and the flashing green appears.
I tried capturing some flash logs but do not see anything suspicious. All the arm checks are on.

2 Earlier, there was the odd occasion when the arm would work and I was able to run the motors (props off), but the throttle was only active up to mid-point (approx 1500) and then raising it beyond that there was no increase in speed. I checked the radio settings and do not see any reason for this and I have done the esc calibration via the radio and the motors would accelerate all the way up to full throttle.

You will always get unexpected results without props.

Make sure you have ARMING_CHECK = 1

Set LOG_DISARMED = 1 and try your arming process again then upload that log.
Then set LOG_DISARMED = 0

More info for case #1:

If I arm using the throttle/yaw and position the stick in the absolute bottom right corner, then the arming fails. However, if I add a very small amount of throttle as I arm, by lifting the throttle stick a small amount, then it arms as expected and the motors spin up.

According to the radio, throttle at zero = PWM of 988
According to MP, ch3in = 982 (after radio calibration)

ARMING_CHECK = 1
ARMING_RUDDER = 2

MOT_SPIN_ARM = 0 (or 0.1)
MOT_SPIN_MAX = 0.95
MOT_SPIN_MIN = 0.15
MOT_SPOOL_TIME = 0.5
MOT_THST_EXPO = 0.65

Does it trigger the Radio Fail safe (by throttle) when you arm? If the throttle value fall under the throttle value you set at FS_THR_VALUE, it will trigger the Fail Safe.

Good pick-up by @bigboy061293
FS_THR_VALUE needs to be at least 30 less than RC3_MIN

RC3_MIN = 982
RC3_MAX = 2006
RC3_TRIM = 982

FS_THR_VALUE = 960

So I will try reducing the value to 910

FS_THR_VALUE = 910 makes no difference (no failsafe msg)

I noticed that once I get the motors to spin, when I reduce the throttle close to zero, then the motors stop with the disarm beep.
My understanding is that the motors on a quad should never stop spinning if the throttle is moved to zero. I suspect this could be my issue.

I tried :
MOT_SPIN_ARM = 0.15
MOT_SPIN_MIN = 0.2

Again I did not see any change of behaviour.

This is because you havent done a take off - and so DISARM_DELAY or zero throttle cause a disarm.

It will only NOT disarm once flight is detected.

Here is the log file. I armed (no apparent errors), led went to solid green and then after 1 second it disarmed,
2023-05-22 14-15-30.bin (696 KB)

Change your DISARM_DELAY to 5. I had the same problem some time ago using 2 seconds.

FIXED! Thank you.
This param was 1 which is not enough time to raise the throttle for take-off before the disarm kicked in.