I prefer on site notification once there is a problem so people know about the issue before starting to click and panic. That's the best solution if the problem is easy to solve in few hours but if the problem is quite big then better to announce about a maintenence in the social media so people take on consideration that downtime.
Anyway in this case it is not a big deal and the problem is solved.
Any maintenance with considerable time of no availability for using the platform needs to be announced officially on the website. The website should be a first place to have announcement about it for users. Then social media channels of a company will be other places for such announcements because some people don't use social media and they need to know what's going on when visiting the site.
It's not like a big issue for deploying a Maintenance message on the website while it is helpful to avoid panic in user community or even just some users.
I agree that there should be a notification whenever maintenance is going on so users know what's going on.
However, regarding withdrawals for one of their available coins, they should temporarily disable it so players can't select that coin for withdrawals. That should be enough to prevent players from panicking, as the process is usually quick, but this time it took longer.
