Structural engineers always tend to go OTT with their advice and want everything checked and confirmed.
If it is a problem now, ie the bay has recently started to move and is likely to move more, then it tends to be evident. and then you need to deal with the cause - which could be one of several things.
If the problem is not current, and its an old crack from some normal movement (which is more common) then you just have the crack pointed up as per above. The trick here is to have it done by someone with a clue, who will blend the repair in to make it look like its nothing and not sticking out like a neon sign to any surveyor
You certainly should not need to go to the expense of underpinning foundations or reinforcement to the wall for a trivial crack.
Now if you have a potential buyer, and they have that report, then they have the upper hand to either want you to carry out whatever is recommended, and spend lots of money doing so, or they can ask for a price reduction and take the risk.
So you need to decide to do that, or just put it back on the market and see if another buyer is interested.
Bare in mind that any significant work such as underpinning raises red flags for buyers and insurers and you need to declare it in any sales pack