Having dealt with numerous brands of machines over more decades than most of you have be alive, let me add two cents worth to this string. More times than not, if the wrinkle is on the rear side of the lower portion of a boom assembly, the cause was a forward impact with something relatively solid. Likely, the point of impact was on the same side that has the bend or at least the side that has the most bend.
In my experience, most of these I've seen were in snow removal areas and many used a wide blade or bucket that was much wider than the loaders.
The hardest to diagnose have been the Rhino brand and Amerequip loaders with curved booms. usually those loaders will bent just below the gussets where the lift cylinders attach.
I'll ask if this brand of loader has a gusset where the lift cylinder attaches? If so, is the bend between the gusset and bucket pivot pin location? If you answer is yes to both of these questions, I would give about a 99% chance someone has hit something somewhere.
If you send me a message, expect a long delay because some of us geezers don't spend much time doing the internet stuff.
Now, if this isn't worth the 2 cents, then just call it free advice which is worth the cost=nothing!