Pi2's GPS lost lock for 48 minutes and its clock drifted by 64.7 microseconds starting at 21-05:50. The pi2's local clock drifted in speed roughly 22 parts per billion

The above is a graph of the pi2's local clock state. You can see that chrony continued to use the last PPS value while the root dispersion value (not shown) increased.

The above is a graph of the local PPS data - there's no data from the PPS between 05:50:05 and 06:38:57 (GPS module lost satellite lock)

Local stratum 1 peer configured (offset has opposite sign due to how chrony's logging works)

Another stratum 1 peer, from the other system's perspective (ntpd classic)