You could possibly be encountering a dhcpcd bug mentioned here: PiAware won't reconnect to wifi network if it drops off (warning, long and confusing thread, it took a while to work out exactly what was breaking)
… which is related to dhcpcd attempting to defend the assignment of its configured IP (perhaps in this case because the DHCP server has reused the IP elsewhere) and then crashing.
I’m not sure what sdcard image you started from. The piaware sdcard image includes a fixed dhcpcd package, but I don’t think the bugfix has made it into the upstream Raspbian images yet, so maybe that’s the cause of things going bad.