"What is unnerving is the number of targets that I get alerts that I never see, even knowing where to look."

Yep, commonplace with me. A major value of Flarm is awareness of nearby traffic and using that to stay well clear, especially when not visual.

I was happily leeching a couple hundred feet below a buddy when Flarm dropped the target.

I promptly left the the thermal. We arranged separation on the radio. Flarm contact remained intermittent.

Later inspection of the other glider showed the antenna was partly detached with the tip touching the fuselage. It's been refastened and will be monitored.

Need to make an incident report.