Notesnook is hostile towards the VPNs recommended by PG.
I propose removing Notesnook. They are hostile toward VPNs. When accessing Notesnook from Mullvad, you cannot change your account password because api.notesnook.com returns a 400 error for requests from Mullvad.
Notebooks
Not only do they reject VPNs, but they also display a fake reason of “Wrong password,” even though the actual reason is that they are rejecting the VPN.
have you tried reaching out to them to perhaps whitelist some of those Mullvad IPs?
Just curious, but why would they whitelist the Mullvad IP’s after clearly choosing to blacklist them in the first place?
Probably because mullvad it’s not blacklisted directly, it’s more likely some server reputation that got flagged because of abused use.
It happens with every VPN.
Why would a company that touts privacy bock any VPN?
To them, they’re not thinking about “Oh, let’s block VPNs, we hate users being less identifiable and gaining privacy from their ISP”.
They’re thinking, “these IPs are being used for abuse, block them as a step to mitigate it”.
That is unfortunate if true.
Anecdotally, the mullvad server I use isn’t blocked, so it’s not just a blanket ban of Mullvad exit IPs (which they could very easily facilitate since those addresses are published). It’s certainly to try and stop abuse like others have commented already.
This is false. We do not ban any IP addresses (aside from those that break our rate limits) or have any kind of VPN ban. We do use Cloudflare which might be blocking these IPs but that is out of our control.
In fact, using a VPN to circumvent network blocks is recommended by our support.
As for changing your account password, we had to temporarily disabled due to a critical issue. It should be enabled soon.
removing Notesnook for STILL NOT SUPPORTING AUTOMATIC LTR RTL SWITCHING, on the other hand, I strongly support 
Smwrt advice!
I stopped using it after they put basic features that were free behind a paywall.