I have a suspicion that Bootloader_Host_GUI expects the flash row size of 64 bytes (as for PSOC 4 devices), but the CY8C4045AZI-S413 has the row size of 128 bytes (which I can see looking at the contents of bootloadable.cyacd). Could someone please confirm or deny this?
Found the problem: the error actually meant that the bootloadable's address in flash overlapped the bootloader. I did not rebuild the bootloadable after having made some changes to the bootloader, which resulted in its larger size. My bad.