That's not enough to exhaust your DHCP pool size of 190 addresses (which could have prevented new devices from acquiring a lease once your pool would have been exhausted).
How is your Pi-hole machine connected to your network?
Is it perhaps connected via wifi or sitting behind a switch?
Wireless connections are less stable than wired ones.
In addition to noise and congestion from other networks or household appliancers, your Pi-hole host's OS may also decide to deactivate its wifi interface when entering a power saving mode.
Do you observe the same behaviour when using a wired connectiion for your Pi-hole host?