Cracked ceiling but can't find joists

[Chill-Pill]

Hi all,
I've got horrendous cracks in my living room ceiling.
Today is the day to tackle em so I've used a multi tool to grate out either side of the crack which I will fill with a lightweight flexible filler.
On the first bit I've started I can see that on one side of the crack the plaster board has some give so am assuming that's what's caused the cracking.
Decided to chuck some screws in there to hold it tight to the joist but every one I've screwed in doesn't seem to have a joist behind it.
Has someone boarded it and left the ends of the boards floating? Scratchy head time

 

[foxhole]

It’s not uncommon .

 

[Chill-Pill]

Oh no.. I hope that's not the case.
I've probs made the problem a hundred times worse then as I've gouged out a tramline to fill back in. My husband is going to kill me.
Oops.

 

[Chill-Pill]

Is there a glue strong enough to fill the crack and hopefully glue both edges together would you know...

 

[foxhole]

You could use coving adhesive, goes on like filler but contains adhesive , keep it thin as harder to sand.