It sounds like this might be a premature failure; it may be under warranty.
I would contact the installer, distributor and manufacturer, pose your questions, and negotiate a settlement with one of them.

Keep in mind that this might be a serious issue not to be ignored. Do you have functioning smoke and carbon monoxide (CO) detectors in your home?

SR

They all have cracks. Over time (many years) the cracks will migrate through the fiber board and then pieces will fall and collapse.

It is subjective as to the lifespan of the combustion chamber liner, If it is many years old (15+ on WM) and it looks bad, replace it, if it looks like it might fail, replace it.

WM is very easy to do. Less than $100 for the kit and if you're DIY inclined with good technical knowlege, it can be done by yourself - it just takes time which is why big $$ often for labor.

follow up for clairification to the OP

- this is NOT in any way a safety or warranty issue
- they form visable surface cracks in the LDCFR (target wall etc.) after as little as 1 month of use, this is NORMAL
- your boiler is NOT old enough to warrant a replacement of the LDCFR
-First tech is trying to extort $$, second tech is likely being honest