Star Wars has revealed several ways the Jedi can lose the Force, both in canon and Legends. When Luke Skywalker met Yoda for the first in The Empire Strikes Back, the aged Jedi Master gave him a briefing on the Force. "Life creates it, makes it grow," Yoda explained. "Its energy surrounds us and binds us." According to Yoda, the Force is the power of life itself, and it permeates everything that is. Given that is the case, most viewers assume it is impossible for someone to be cut off from the Force.
This is not the case. In fact, the in-universe book Chronicles of the Jedi hints it is not uncommon for a Jedi to be cut off from the Force, or alternatively for this connection to become unstable. According to this book, which purports to be compiled by a Jedi Master, there are multiple avenues to restore this sacred link. "Jedi counselors are specially trained to help others work through traumatic events when individual meditation is not enough," the book notes. If it is actually quite common for Jedi to lose access to the Force, then it is naturally intriguing to look at all the known scenarios where beings have lost (or been stripped of) their Force connection.
6 Some Jedi Can Lose The Force Through Disease
The only known canon example of a Jedi who lost access to the Force is Sskeer, a Trandoshan Jedi who lived during the High Republic Era. Sskeer lost the Force through disease, suffering from an illness that affects his species called Magrak Syndrome. This causes a Trandoshan to experience rage and aggression, and the mind's attempt to stave off the encephalopathic disease makes it impossible for him to connect to the Force. Sskeer ultimately came to understand even this was according to the will of the Force, however, because the timing - occurring just as a species of Force predators called the Nameless were unleashed on the galaxy - made him the only Jedi who could stand against the growing darkness.
5 Jedi Can Lose Their Force Power Through Injury
As powerful as he may have been, Darth Vader's potential was actually reduced because of the injuries he sustained on Mustafar. Darth Vader's powers were diminished precisely because he was now a cyborg, more machine than man, with so many of his limbs replaced by artificial ones. As explained in Star Wars: Episode I - The Phantom Menace, Force-sensitives are symbionts with the midi-chlorians living within their cells. When Anakin lost his limbs, he naturally lost the midi-chlorians living in those cells as well.
4 Jedi & Sith Can Be Closed To The Force
It is possible for a Jedi to cut themselves off from the Force, so they cannot sense anything through it. Luke Skywalker, distraught after Ben Solo's fall to the dark side, retreated to the planet Ahch-To and performed this feat; not only could he no longer be detected in the Force, he also could not sense anything else going on in the galaxy. He had no idea Hosnian Prime had been destroyed, and he did not sense the death of his friend Han Solo. Force ghosts like Master Yoda presumably could not visit Luke until he reconnected to the Force.
In canon, a number of other Jedi have attempted to cut themselves off from the Force, or at least reduce their awareness of it. During the High Republic Era, Jedi Master Elzar Mann - shaken by his vulnerability to the dark side - cut himself off from the Force for a time; according to Mike Chen's novel Brotherhood, Anakin Skywalker did the same at one point when he was just a Padawan. Jedi Knight Cere Junda suppressed her connection to the Force during the Dark Times of the Empire's reign, fearful she would fall to the dark side.
3 A Jedi Can Lose The Force As They Lose Their Sense Of Balance
Jedi: Fallen Order's protagonist Cal Kestis opens with a reduced ability to draw upon the Force, which is said to be because he has lost all sense of balance in his own mind. It isn't just that he has closed himself of from the Force; it's that the confusion and uncertainty in his own mind limits his ability to draw on it. It is only as he regains a sense of balance, and most notably faith in the will of the Force, that he finds himself able to use the Force and practice long-forgotten skills.
Something similar may have happened to Obi-Wan Kenobi during his self-imposed exile on Tatooine. The Obi-Wan Kenobi Disney+ opened with Obi-Wan struggling to trust the Force, and he could barely draw on it - as shown in a horrific duel against Darth Vader, in which the Sith Lord mocked Obi-Wan's powerlessness by throwing him around telekinetically. The events of Obi-Wan Kenobi saw the Jedi Master regain his trust in the Force, however, and he was subsequently able to beat Darth Vader in a rematch.
2 Sever Force Can Cut A Jedi Off From The Force
This is presumably a variant of an actual Force power seen in Legends, called "Sever Force." There, it was portrayed as an ancient punishment, a way to ensure fallen Jedi could not pose a threat once again. Sever Force was used on a spectacular scale against an entire race, the Yuuzhan Vong, who left the galaxy - only to return centuries later as invaders. The Jedi had no knowledge of their history, and so the Yuuzhan Vong's absence in the Force posed an intense philosophical problem for Luke Skywalker and his new Jedi Order.
Although the Yuuzhan Vong are officially non-canon, they almost made their way into Star Wars: The Clone Wars. An unfinished "alien abduction" story would have seen a single Yuuzhan Vong ship probe the galaxy ahead of the Clone Wars. These Yuuzhan Vong were very different, however, with their absence in the Force removed because George Lucas didn't like that element. Sever Force apparently didn't fit with his interpretation of the Force in Star Wars, an important point to note.
1 Ysalamiri Can Cut A Jedi Off From The Force In Legends
Timothy Zahn's Legends "Thrawn trilogy" introduced creatures known as ysalamiri. The Force simply doesn't work around ysalamiri, with Jedi unable to sense it - and even manifestations of the Force such as Sith Force lightning disrupted by it. Again Lucas was uncomfortable with the ysalamiri, and later books clarified that the ysalamiri are not a "dead zone" in the Force - rather, they emit a field that suppresses the Force around them. This was developed as an evolutionary defense mechanism, given they were hunted by predators who used the Force.
Ysalamiri have technically been canonized in Star Wars, because sculptures representing them can be seen in Grand Admiral Thrawn's art collection in Star Wars Rebels. Thrawn is set to return as a major antagonist in The Mandalorian era, meaning this idea could be picked up again. If so, Force-sensitives like Ahsoka and Baylan may find themselves at a disadvantage when they go up against Thrawn.