This clearly is the killer.
So the new kernel on scarthgap exceeds the memory which u-boot has allocated for loading it. Good news is that it then fails to boot, and rollback saves you. Bad news is that this is probably hard to fix in place, as reflashing an updated version of u-boot on live devices usually creates a single point of failure.
The most practical advice would be to inspect your kernel configuration, and see if you can trim it down enough to fit into u-boots loading region. Usually the default kernel configurations leave quite some leeway for such.
Greetz,
Josef