It would be a shame if you entered grades and came back later to find them gone. this scenario was recently reported to me. The word from Canvas support was that an out-of-date browser (Firefox in this case) was the culprit.
Regardless of the browser you use please make sure you keep it up to date. This is important as Canvas is a web-based tool.
Contact the Helpdesk if you need assistance updating your browser(s) on Lawrence-owned computers.