If you’ve recently upgraded to macOS Mojave and experienced stability issues using Sequel Pro, you’re not alone.
Unfortunately the development of Sequel Pro seems to have been frozen, but seems to gather speed now again with the support of the community. They’re rebuilding the underlying build and server structure and hope to be up and running soon again.
Until a new official release is made, you can download and install the nightly build of Sequel Pro using homebrew:
brew cask install homebrew/cask-versions/sequel-pro-nightly
As another option you can download a unsigned build at your own risk (!!) by khanhicetea here:
Hoping this fixes most of your problem and that a new official release of Sequel Pro will appear soon.