Log contains: "Try restarting the process to restore its attach capability".
Most probably the /tmp directory was cleaned.
When attaching to a jvm, the steps we take are the following:
1) agent sends signal to monitored process
2) monitored process creates socket file in /tmp
3) agent connects to this socket.
Step 2 is only happening once. If the socket file is removed (e.g because the tmp directory is cleaned), then it is impossible to attach to this jvm afterwards.
The only fix is to restart the monitored (or rather to-be-monitored) process.