Isn’t too old? Snap version seems to be 1.0.1 (from far 2016) while I can download from website 1.3.3 today (dec 2018)
Luca
alan@hal:~$ snap find simplenote
Name Version Publisher Notes Summary
simplenote-jamiebennett 1.0.1 jamiebennett - The simplest way to keep notes. Install with --devmode.
simplenote 1.3.2 snapcrafters - The simplest way to keep notes.
Looks like you have simplenote-jamiebennett installed, which hasn’t been updated. You probably want to switch to simplenote - and perhaps @JamieBennett may want to un-publish his 
1.3.3 will landed in the simplenote snap very shortly - possibly by the time you read this.
Done.
It was part of a snap tutorial I published but happy to retire it.
Thanks everyone guys!