Could be the case...it has definitely been a pattern over the years. When UCONN loses a game, it's almost always close or comes down to a final play (or two). UCONN has struggled the last several years in the (few) close games they've had. Execution down the stretch hasn't been there (all of the mess ups in 2013 vs. ND, Williams turnovers vs. ND this year, Chong bad shot last year), plus there has been some questionably decision making from the coaching staff in tight games (sitting Stevens in the 3rd, FSU in 2016-17 was very poorly managed at the end of the game). I don't think it's a factor of coaching as much as it's that players just have almost zero experience in single possession games. You can simulate it in practice, but it's a lot different in real games...especially with a lot on the line and everyone expects you to win.
If a team can hang, usually UCONN goes on a run to create separation and then wins without a whole lot of last minute drama (ex. Baylor 2014, championship vs ND in 2015 and regular season 2018, Maryland in 2016 and 2017, Texas this year). If they get down to a final possession, other teams are usually flying high with confidence and they have playmakers who can finish the job (Orrange 3 in 2015, Morgan William last year, Arike this year).
Another thing worth noting is that UCONN's style of offense doesn't cater to individual playmaking..it's all based on ball movement and getting the best look. You almost never see a player going one on one like William or Arike did. The team offense is wildly successful for UCONN, but it can be a double edged sword in close games where there isn't a player who you can give the ball to and tell her to create and win the game for her team. Maybe Williams will be that player for you guys like Taurasi was back in the day, but one on one play can be extremely useful at times even if it's hurtful at others.
Also, to UCONN's credit, the ND game this year wasn't really lost by UCONN....they were beat by a team that stepped up to the plate and played great basketball on both sides. Arike hit a difficult shot with 1 second left on the shot clock to create separation in regulation and then nailed a tough contested jumpshot to win the game. And UCONN didn't falter when the game looked lost for them--Collier and Dangerfield hit massive threes end of regulation and in OT, Nurse got the steal and layup, and even on the very last possession, UCONN almost scored on what would've been a miracle pass and bucket to force double OT (not sure if it would've counted or not).