I have the reverse problem of this question: How to fix virtualbox's copy and paste to host-machine?
Sometimes, I am able to copy-paste from guest to host (both Ubuntu), but not from host to guest, even though Shared Clipboard is set to bidirectional. For example, yesterday both directions were working fine, and I paused the VM for the night. Today I resumed work on the VM, and host to guest copy paste no longer works.
