Is it normal that 2FA is only valid for 2-3 days?

It should last a lot longer. Do you switch to different networks, use a VPN or similar? My guess is that that is causing the issue. On my phone I almost never have to enter the 2FA code. It most often only using my home wifi. On my work computer that several times per day switch between my home network (in Sweden) and work VPN (in Germany) I pretty often have to enter the code even if I check remember this browser.

Nope, no VPN.

After it worked for months I am now back to multiple times a day since yesterday.

Yes, something changed now, but it's strange, while logged-in on the forum, opening Web logouts.

I can confirm issue. This has started recently. Before that, I stayed logged in for months. 

Now I have to always login but it's not asking for the 2FA.