the frame lock % on the status page and the packet error rate in the tuner app are completely different metrics.
The packet error rate in the tuner app is how many packets were received that failed a crc check. When you say you "missed one packet" - that just means only 1 packet out of those received failed crc. In normal operation, you may lose a few packets.
The frame lock percentage on the status page actually measures the stablity of the frame lock itself. If you have local interference, or low SNR, then you will intermittently lose frame lock. When frame lock is lost, no packets are received, and these "lost" packets are not counted at all in the previous metric (obviously - the system did not even see them). The frame lock % is the percentage of the time you had frame lock. In normal operation, you should expect to have 100% frame lock. (thats why the balloon is only green if the frame lock in 99%+).