Someone else just reported a similar issue here in the Forums – could you create a bug report regarding that in the support tracker?
I unfortunately haven’t been able to reproduce this, but with a bug report in the support tracker we can get Jamie to take a closer look and sort out what’s going on there. Thanks!
In the meantime, you can manage your database/s in webmin>servers>mysql database…
I am the other user with this issue and I whilst in also cannot use virtualmin for database management without 404 errors, I have no problems when I use webmin to do it.
Mine only started doing this recently after an upgrade from GPL to pro.
I suspect it could also be Mod security causing it but in all honesty I am not sure because I can’t find this error in the logs