With the way that the ATP has redesigned their rankings system, we will continue to see this back and forth occurring. The points system as it now currently stands over-rewards the challenger system like crazy (this coming from a huge challenger supporter), and it is just ridiculous. For example, a challenger win is either equal to or exceeds the points given to a semifinalist at a 250 event or a round of 32 at a best of five set Grand Slam, which is just crazy. So whoever wins next week's Leon challenger with a current 359 ranking cutoff and where the highest ranked player entering is 136 will get more points than a semifinalist in Dubai or Queens or a player that wins two matches at Roland Garros. Thus we will continue to see unknowns crack into these 65-120 positions, and then eventually slide back down after a bunch of main tour losses to be replaced by other players who had to pick up easy challenger points.
It's insane, and the ATP really needs to go back to not excessively weighting challenger results...
Like I've been saying all along. Take a tip from the American Sports Leagues. Completely separate the tour and the Challenger level. Just basically make a cutoff at the end of the year of 100 players that will play ONLY tour level tourneys. They get decent money from participating in the 1st rounds of Masters and slams anyway, doubles etc... plus there's the 250's which are a decent source too. Too help tighten the calendar just compress some of the tournaments and have like 2-3 minor 250s taking place every week so that everybody can play and have realistic chances of getting match wins.
And after 6 months or so, make that cutoff again based on the rankings. Whoever performed the worst drops to the challenger level. Whoever won the most points in challengers advances at tour level.
It's super simple and it will make things that much interesting.
The current rankings are flawed imo.