One of the batteries from the FLy More Package could not be charged.  I tried swapping the slots but it does not help.  Is there some thing wrong with the battery?
Please look at the video here:

try power cycling it?  press once.. pause for like half sec then press and hold... i think?  battery has multiple modes... it may just need a waking up

be patient... it;ll charge eventually.. if after 2 hours still the same then there is a prob..
the charger support simutenous charging, but there are some conditions for it to work if not met, it will charge the battery that requires the least time to charge 1st then move on to the next one

it depends on many things.   but the batteries have many modes and protections.. .. my batteries refuse to charge if they are a bit too warm.. or if they got fatally damaged... or maybe it's hibernating or in discharge mode...

My batteries will not charge immediately after flying, possibly because they are too warm?? If I leave 30 minutes there is never a problem

I am not able to watch the video for some reason. Have you tried to charge the battery when it is inserted in the Spark? What is the lights status?

I thought something was wrong with mine too but these batteries somehow determines when or what order to charge. Just leave it on there and it will charge.

its not showing  , that the temperature is wrong , it's not showing anything  hmm . it should  charge them both at once .

Have you tried hooking up the spark and the battery to the DJI assistant 2 to see if the firmware needs to be updated ?

If the remaining charge left in batteries is not close enough, the charger will charge them sequentially. It is explained in the charger documentation.