RSJ protruding above floor boards

[Rimrogs]

We recently moved into a 'tired' 70's dormer bungalow.
I was laying a laminate floor in an upstairs bedroom and noticed the floorboards had a high spot. This coincided with an RSJ which spans the double garage below. I had to lift and rebate the boards as the laminate wouldn't lie flat. I can only assume that the joists have dropped (rather than the RSJ has risen!). On closer inspection (looking in from the bedroom floor) the joists are rebated to fit into the RSJ but most are below the top of the RSJ itself - hence the ridge.
The RSJ is clad in 'Asbestolux' inside the garage and it looks like some of this has been used to shim the joists originally.
Do these joists need reshimming? Is this the cause of the ridge in the floor? Are there any complications if the asbestolux has to be disturbed to get at the joists from the garage?
I've just realised that the airing cupboard is lined with the stuff as well.
Any help welcome

 

[noseall]

your probably right about the packers (shims). the joists have probably dried out and shrunk a little and the packers come loose or are missing completely. re packing with eternit slate may help, and you can re-clad the steel beam with two layers of plasterboard, or a single layer of 12.5mm fire board. both would have to be skimmed.

having said all this its only a speculative diagnosis having not seen the job.
p.s it may help to fix the packers down this time with maybe silicone or similar.