Got this answer from Mbed support.

Thank you for reporting the issue to Mbed Support. We are also aware of the online compiler exporting error and our engineering team is working to resolve this issue ASAP. Sorry for the inconvenience.

On the plus side only the online compiler is having issues, all code repositories are still available. That means you can use Mbed CLI during this time to continue your work. Mbed CLI is the tool behind the online compiler that we use for compiling your programs. Using Mbed CLI you can trivially move programs between your online repos and offline for development. To bring your code down to your computer simply run mbed import <URL of Program> and the code will be pulled down to your computer. You can use mbed CLI with windows, OSX or Linux, the compilers for GCC, IAR and Keil are all supported, and if you're interested there is even an mbed export option that will let you export your program to Keil, IAR, Eclipse and many other IDE's. In addition mbed CLI works with both mercurial (os.mbed.com) and git repos (github.com).

Here is the getting started with mbed CLI YouTube playlist: https://www.youtube.com/playlist?list=PLiVCejcvpseuWWmJc9uELYww-xindjZCH

Here is the full documentation for Mbed CLI: https://os.mbed.com/docs/latest/tools/installation-and-setup.html

Again, we apologize for the downtime, and while we hope a similar event does not happen in the future, just in case it does you can use Mbed CLI to continue your work without interruption.

Please note that you must commit your changes to your repositories for them to be seen. So it is considered a best practice to always save your code in the online compiler by committing frequently!