Error message uploading mission plan

Hi. I’m using QGC 3.4.3 with Pixhawk 1 running PX4 1.8.0dev. When uploading a mission, I get the following error message: “Error loading Plan file. The following required keys are missing: version, circles, polygons.”

What does this mean? The mission seems to upload OK, so I believe the mission will run, but is this a serious issue? And how do I solve it?

I think all my missions were designed with PX4 1.7.3. Could that be the reason?