Onionperf guard clients show dropped_ts missing key bug when visualizing multiple days

I have found that the serie-7 onionperf a-clients have the dropped_ts missing key issue.

This happens when the guards for a circuit have a register a DOWN event instead of a DROP.

"current_guards": [
              {
                "country": "br",
                "down_ts": 1656636758.69,
                "fingerprint": "27C6A5DA5D06113D0E08C5C2BE5527BA9A0F1192",
                "nickname": "RjPi1",
                "up_ts": 1656637380.47
              }
            ],

I wonder if this behavior can be considered normal and we should update the code or we are parsing events wrong.