I have sometimes problem with managed speed mode on landings. It happened to me today when landing at Reno Tahoe KRNO, and most recent at Halifax CYHZ and St Louis Lambert KSTL, though all settings are very the same as other landings (no problem with managed speed). Aircraft passed Decel point, approach mode activated, ILS intercepted, but the speed on approach is way over 280 kts, impossible to deploy Flap 1, using air brake also not help. Distance to runway less than 15 miles. Got crazy!
I noticed that when Decel points are way to close to runways and STAR are missing on route, I always have this problem!