You have reported the lower right blue led of ‘24V_MOTOR’ is on so that is good to know.
This will be a problem, maybe our main clue.
The blink rate for v40 is 5.75 sec/blink for the released version which basically matches your observation of ‘about 6 sec’. What really matters in firmware daycode of course.
The ‘official’ v40 will have in ‘rostopic echo /diagnostics’ a firmware date code of 20201209 but I am thinking that is not our problem but still, check that to be complete here.
Not yet stated but verify the 2nd led from left in row of leds that says 12VM is on and in fact verify all 4 leds to the left are on solid and you have already said the right hand LED, ‘STATUS’ is looking normal at 6 sec per blink.
There are some new blink codes in the firmware that show up on the ‘STATUS’ led that may offer some clue as well.
This page: Verification | Learn Ubiquity Robots and ROS in ‘Part 5’ shows some new blink codes that may show up right after power-up so see if after you power up OR you push the ‘RESET’ switch on the MCB that is 5cm below the left, ‘AUX’, 4-pin power jack. Verify that you only see the normal blinks happen and you don’t see a sequence of blinks described on verification page.
Next I would like you to try our recent ‘motor selftest’ feature. See if you can find a standard 0.1" jumper commonly used for option switches and so on on PC boards. If you have such a jumper turn off the magni and BEHIND the MCB board just about in dead center of the board put that jumper on the middle to lower pin only accessable from battery compartment. This is P706 and if the TP4 lower pin is shorted to the center pin (ground) the v40 firmware will do a selftest, part of which is to try to turn the wheels on its own. If you put the robot on a block so wheels don’t hit ground, you will if it works have the wheels rotate one way then another (it is a small rotation of around 10 degrees each way).
Lastly for sake of being complete we want to inspect all wires from each motor cable going into the back of the MCB and tug wires slightly to verify they really are screwed in nicely. This is 9 wires per wheel.