I can only think of two specific examples of this in the movies, both of which would seem to have rational explanations.
In The Empire Strikes Back, Luke uses the Force to retrieve his lightsaber when hanging upside down in the Wampa cave. In this case, the difficulty was due to Luke's inexperience and lack of training as a Jedi. It was very difficult for him to achieve. You see him relax his arms, close his eyes, focus and try again, after which he succeeds. I've found several drafts of the script that seem to back this up. Interestingly, Obi Wan speaks to Luke in these versions.
- EXT ICE GORGE - MED SHOT LUKE - DUSK
Luke pulls himself up, grabs hold of his ankles, and futilely
tries to unfasten the thongs. Exhausted, he drops back into the
Luke spies his laser sword lying near a pile of his discarded
gear about three feet out of reach. Reverberating through the
gorge, the growling and crunching sounds of the approaching ice
monster can be heard. Luke desperately strains for his sword.
Quietly, almost a whisper, Luke hears old BEN'S CALM VOICE.
BEN (Voice Over)
Luke, think the saber in your hand.
Luke focuses on the saber as the huge monster's feet crunch
closer. Luke's hand strains toward the weapon, his eyes squeeze
tight in concentration.
Gotta relax, relax...
BEN (Voice Over)
Let The Force flow, Luke.
Just as the ice monster looms over Luke, the light saber suddenly
jumps three feet into Luke's hand.
Secondly, in The Force Awakens, Rey and Kylo Ren are both attempting to pull the same lightsaber at the same time, resulting in the Lightsaber shaking, not knowing which way to go, until one of them successfully overpowered the other to retrieve the saber.
EDIT As noted by @CBredlow in the comments, Obi Wan also has trouble retreiving Qui Gon's lightsaber when hanging over a (typically Star Wars) bottomless pit. It often seems that Jedi have most success retrieving objects when using their arm to focus themselves. This would be difficult when hanging on for dear life. Sadly the script is much less descriptive for this movie, and I don't have access to the novelisation to get a relevant quote to back this up.