My friend can no longer heal me... What gives?

[Luke]

So my friend no longer as the prompt "Press F to heal" when he looks at me. We don't know why this has occured and he hasn't made any recent changes to controls or otherwise. We even both restarted our game but to no avail. I can still heal him.

What's going on?

[Levitater]

You can only heal friends when they are critically low on HP. How much health did you have left?