If it suddenly stopped working after you were "messing around", did you by any chance happen to include descriptions when setting up static IPs?
If so, you might have run into the same bug that I just did - it's possible to enter characters that screw up the dnsmasq config and prevent it from loading (which will prevent clients from getting DHCP leases).
Double quotes are one example, so it'll happen if you put something like:
65" TV
The part that makes it tricky is that unless you check logs after making changes, there's no clear indication you've broken things until your leases run out and devices that weren't manually configured start dropping off the network.
Manual config for gateway / netmask / dns seemed to be enough to connect to fix things without needing to reset config.