How often do charging networks offer free charging and do they announce it?

A few months ago, I was in Canada and used a charging station from Electrify Canada. It was free. Then, this past weekend, I used one from Electrify America, and it was also free. When they offer free charging sessions, is it for all their stations, or only some? And do they announce it anywhere? I checked both times but couldn’t find any info on why it was free. My question isn’t just about Electrify, it’s about any charging network that offers free sessions.

Recently, Electrify America (maybe Electrify Canada too?) gave out free charging sessions due to a software update they’ve been doing. Now, the charging fees are back to normal. Some charging networks also offer free charging on holidays or special occasions, but they don’t always announce it to prevent overcrowding at charging spots just for free power.