Intentional. Players can only upgrade one base at a time. The option to cancel represents the base currently being upgraded. Players can remotely stop that upgrade to proceed with upgrading the base they want.
I wished I could help but this is out of my control sadly. FP does not know what causes this or how to fix it yet. Since the code doesn't run for players in limbo I can't attach any fixes to it.
I will keep digging around in the meantime.