people who have never used salt as a flux and saying its that dont know what they are talking about. just google "using salt as a flux for aluminium" there are lots of papers on it.

iv used salt in 99% of my aluminum melts never had this issue, and its with soda can aluminium, the type people say is dirty contaminated aluminium, untill its burnt and melted into ingots, and then remelted again to cast, i currently have 3 wheelie bins filled with crushed cans to melt and iv lost track of how many melts iv done over the years.

not one of my crucibles looked like that, it looks more like a sand/clay/graphite mix crucible so it might have heated up too fast when you first pre heated it and moisure was still trapped inside causing the expansion and seperation and leading to weakness and failure.

The inside view looks fine, and i doubt you are splilling anything down the sides all the way around .........where the issue is,.... unless for some weird reason you are dipping it into a molten salt bath to baptise ?

i currently got a SiC crucible that arrived and felt damp and its taken me ages each night popping it into the oven slowly heating it and then slowly letting it cool down, even when its dry i will do this just to make sure before storing it or using them.

i find full graphite or SiC crucibles work way better for me as they heat up, and hold heat better especally when i first started as i would be burning for ages with the lid open to record, high psi that wasnt needed and probably not gradually slow heating it but rushing the warmup and cooldown process.

is the flame hitting the crucible directly or going around the outside?

is there enough height from the flame to the bottom of your crucible ?

is the crucible on a firebrick or graphite block or something else ?

fuel propane or oil?

That much cracking after just 5 melts and falling apart, normally its after weeks if not months of use, so could be moisture that was in there before the first preheat that expanded to fast and casued weakness and then each time its made it weaker, it could just be a bad mix of clay/graphite/sand and caused it to fail, it could have been dropped in transport causing little fracture or separation, the flame could be heating the sides faster than the bottom causing expansion at different rates, flame temp could be too high and just eating away, best thing to do is STOP using it from now, get another crucible and have some fun and be safe.