My son showed me how to fix this issue. It is the same in Chrome, Edge and Firefox. Safari has a similar method, although it takes more steps. These steps are all for a PC.
In Chrome and Microsoft Edge.
Go to vintagedrumforum.com. Click on the padlock icon directly to the left of the url in the address window. Click Cookies in the drop down menu then click the Remove button, then press the Done button. You can now login to VDF and the login should stick. If it doesn't, close the browser and bring it back up and it should work.
In Firefox,
Go to vintagedrumforum.com. Click on the padlock icon directly to the left of the url in the address window. Click on Clear cookies and site data in the drop down, then click the Remove button. You can now login and the login should stick. If it doesn't, close the browser and bring it back up and it should work.
The steps are the same on Chrome and Firefox on Android, although a trash can is substituted for the remove button.
I copied this from the Apple site.
Clear cookies in Safari on Mac
In the Safari app on your Mac, choose Safari > Settings, then click Privacy.
Click Manage Website Data.
Select one or more websites, then click Remove or Remove All. Removing the data may reduce tracking, but may also log you out of websites or change website behavior.
It's probably similar on Safari on iOS
When the site had the DNS issue and crashed earlier this year, the cookies for the old site no longer worked for the restored site, but for some reason would never update so this broke the ability to keep you logged into the site.