There is a curious dispute between Croatia and Slovenia in regards to their land and maritime border. It appears to be ongoing since the breakup of Yugoslavia.
Noticeably Slovenia tried blocking Croatia’s bid to join the EU up until 2013, when it appears they stopped trying?
From there on it appears that everyone was okay, even Slovenia, with Croatia joining and staying in the EU even though the issue was never resolved.
In short, other factors, more valuable than the border dispute, must have motivated, or pressured, Slovenia to give up vetoing Croatian membership.
What could have possibly been more important to the Slovenians or its leaders?