I was assuming “beams” was an alternative expression for “lots” and that both refer to the cargo loaded for transport, which Lisanne2000 says are “Holzstämme.” Further, I was reading “maximum limit in height of the lots/beams” as referring to the height to which the cargo could be stacked on, or in, the truck before “strapping.” Finally, I was reading the incorrect use of “beams,” which you rightly note, as resulting from, as Lisanne2000 puts it, “kein Muttersprachler” being “am Werk hier.”
But admittedly, that comment of hers means there’s no way one can be certain about anything: Does “lots” refer to the cargo at all? Is “beams” an alternative term for “lots” or something completely different? If the latter, why are they joined by a slash and not the conjunction “and”? Perhaps Lisanne2000 knows something we don’t (that leads her to think “beams” refers to side-struts of some kind, “Rungen”)? Etc.