FXS breakdown. July 2021.
French version of this document
Discussion and solution in electricmotorcycleforum.com : finally, it was a failure of the controller and it has been repaired by a Zero dealer.

In brief :
The bike is a 2016 FXS ZF 6.5, with two removable battery packs.

The bike was running fine until these days. On July 7th 2021, I have charged the bike during night using a manual timer. The bike charged from 58% to 73% in 1h 30min. Until there all seemed OK.
But when I tried to use the bike the day after, the bike did not start.

Abnormal behavior :

Bike does not start
Bike does not charge
No "click" when keying or attempting to charge
Dash is flashing 1min 30s after keying or after attempting to charge
The red triangular indicator on the dash does not behave the same way when side stand is up or down
When side stand is up, the red triangular indicator says "Contactor error", according to the manual
The dash indicates these errors :

25 Contactor open warning
27 Precharge error
48 SEVCON startup disabe (only once, not cycling)
49 Contactor open disable
58 BMS sensor warning

When trying to charge, the BMS LEDs indicate that the bike is balancing, instead of indicating the SOC

It does not seem to be a problem with the BMS and the batteries, since I have made soft and hard resets of the BMS, tried to operate the bike with only one battery (in case one of the battery had a problem). I have tested separately both batteries in the rear position, then in the front position (with the "blanking plug" in the free position).
As a result, since the contactors are in each of the batteries, it is almost impossible that the contactors themselves are faulty (they could not both have failed at the same time).
It is therefore a problem upstream of the contactors.

More details :
What seems abnormal is in red.

When keying on the bike, no "click". After 1min 30s the headlight turns off and the screen starts flashing.
July 8th: with the bike on the side stand => the red indicator flashes are not described in the manual

Video showing the screen: https://photos.app.goo.gl/UX6R9hTSqynon3Nw7
Video showing mainly the BMS LEDs: https://photos.app.goo.gl/VFfZHfSWQsadhrSU9

July 9th: with only one battery, and since the day before, I have made a soft RESET on the battery BMS (but it has not changed anything)

Video showing the screen, https://photos.app.goo.gl/ksvES1geHbqKE5bX7 with the side stand up => the red indicator flashes are described in the manual and correspond to "Contactor error". The error codes are: 25, 27, 48 (once), 49, 58.
Video showing mainly the BMS LEDs: https://photos.app.goo.gl/MF2gE7koGCBzyc1k9, ob the side stand. LED 1R-2V-3V, that is normal, according to the SOC.

When I plug in the charging cord: no "click". After 1min 30s the screen starts flashing. The bike is on the side stand.

Video showing the screen and the BMS LEDs:
https://photos.app.goo.gl/rWoPzgBo1YowRezT9 from July 8th, with the 2 batteries
https://photos.app.goo.gl/QTqNUP4RQokpk6J39 from July 9th, with 1 battery
In both videos, the BMS LEDs, instead of showing the SOC, show that the bike is in balancing state, which is abnormal.

The bike is a FXS model 2016, with original firmware:

Serial number      2016_mbb_ca1a29_02158
VIN                538XXAZA1GCJ06548
Firmware rev.      47
Board rev.         3
Model              FXS

Logs :
Note that I have almost all the logs for the entire life of my FXS. Detail here. I have also all the logs transformed in text files using the parser. These files are indexed, in such a way that I can easily find any text string in these files.

It was difficult to get the last log since when the screen start flashing the transmission of the log crashes. After several attempts I got it.
Log file in .bin format
Log file converted in .docx format using this parser and segmented at each restart of the bike.
Seems abnormal (appears 3 times in this log, all 3 after the bike failure. But I checked that these lines appear several times in older logs, so they are perhaps not directly related to the present failure):

DEBUG: Reset: Software
BMS Reset Software

Errors on the dash :

Error	2016 manual	2017 manual
25	Contactor open warning
27	Precharge error
44	Kill switch disable
45	Kickstand switch disable
48	SEVCON startup disable
49	Contactor open disable
58	not in the manual !!!	BMS sensor warning

Batteries and fuses
My bike has 2 removable batteries.
On July 8th, while batteries removed from the bike, I pushed on the left (gauche) RESET button of both batteries. According to https://zeromanual.com/wiki/BMS_Reset_Procedure, it should have done a "hard reset". But I do not understand if this works while the batteries are removed from the bike. Anyway, it does not seem to have changed anything.
On July 9th, I have made soft RESETs, but it does not seem to have changed anything.
Video of the resets.

Numbering of the BMS LEDs according to the manual: 1 red, 2 green, 3 green, 4 green.
When the batteries are inside the bike:
Rear battery: the LEDs are visible from the bottom of the bike.
Front battery: the LEDs are hardly visible by removing the saddle, and visible when removing the front left plastic fairing.

I have checked all the 5A and 10A fuses.

BMS LEDs
I have checked in several modes that the LEDs of the 2 batteries are flashing perfectly synchronous. It means that both batteries communicate with some central system.

Short link to this page: https://bit.ly/FXSbreakdown