This is a known bug and happens randomly to any icon put out to the desktop.
They randomly have no text. This is under investigation for quite some time, but there is currently no way to reproduce properly as it is random.
Piru said "While MorphOS doesn't run hosted, it does run in QEMU. This offers all the same benefits as running hosted". So if you have a way to use memory watchpoints this should not be that hard to debug. If that's not possible I would first try to find out under which currently running Task the text disappears: on icon load save text pointer address and text pointer address content in some globally accessible variables (maybe some unused fields in ExecBase) and in kernel after each taskswitch do
if (WatchPointer && (*WatchPointer != WatchPointerValue))
kprintf("** Task %s memtrash **n", SysBase->ThisTask->tc_Node.ln_Name);
Once can suspect that there is some memtrashing involved, which combined with random order of stuff after boot is or is not causing any damage to the text information.
Can't you quit/restart Ambient without reboot? Or for easier debugging: allow a second copy to be running at the same time. Less randomness.