This bug is introduced with the last season’s (season 9) launch patch.
In the season 4 launch patch (Overwatch 2 - Patch Notes), the top 500 leaderboard eligibility of role queue is changed to 25 wins on that role.
Players will now be required to win 25 Competitive matches before being eligible to enter the Top 500 leaderboard for a specific role, queue, or region.
In season 6 (https://overwatch.blizzard.com/en-us/news/patch-notes/live/2023/08), this requirement for role queue is changed from 25 wins to 50 wins.
The number of wins required to appear on the Top 500 Leaderboard has been increased from 25 to 50 for consistency with our other Competitive game modes.
Of course, those changes do not affect previous seasons.
However, at the beginning of the season 9, player’s career profile had a UI redesign. Currently, players who were top 500, but only had 25 wins in the 1-5 seasons (which do not require 50 wins), have their rank number disappeared in the “current” section of their profile. Their ranks are still valid as they are still showed in the leaderboard.
I know this is a minor bug and does not affect gameplay, but it has been over a season, and I hope developers could kindly fix this display bug in the future.