The log has a limit of 200 entries. If there are 200 entries already and a new log entry is registered, the oldest one is deleted. This is necessary because otherwise the log size could grow very large which slows down saving and loading.
EDIT: Fair point. We can make the log size configurable with a warning that having large log size can affect performance.
EDIT3: Good catch. This is fixed in PageProbe 1.11.6+ (available right now). It worked fine on Chrome but Chrome and Firefox seem to produce different element position data for events.
EDIT4: Available in PageProbe 1.16.0+ (right click folder and select 'Refresh Failed Probes')