Yes, there's no minimum time before a retreating faction re-enters ... with the expansion and retreat timed right, it could even reappear immediately. The list of previous retreats seemed to have a full reset with the 3.3 release, but other than that they don't seem to time out.
Priority currently appears to be:
- nearest system in range with <7 factions, no previous retreat since 3.3 release; if no such system...
- nearest system in range with <7 factions, previous retreat since 3.3 release, order of previous retreats ignored; if no such system...
- system in range with exactly 7 factions, picks the system with the lowest influence valid invasion target rather than the closest (may or may not account for previous retreats); if no such system
- cancel expansion, next one has the larger range
"in range" is a cube not a square, but "nearest system" is measured in a straight line.