Why didn't the other Jedi know that Vader was Anakin?
Obviously Vader/Anakin had a massive presence in the Force, so why didn't some of the other force users who encountered him (like Ahsoka, Maul, Jocasta Nu etc) immediately know that Vader was actually Anakin? He masked his appearance, but he couldn't have masked his force presence.
A few reasons.
1.) Everything about Anakin changed when he turned to the dark side... Even his existence in the Force was corrupted/altered.
2.) The overwhelming dark side presence in the galaxy obscured the Jedi's senses.
But there was a darkness to Ahsoka's meditations now that she didn't like. It was as if a shroud had been wrapped around her perceptions, dulling her vision. She knew there was something there, but it was hard to make out, and she wasn't entirely sure she wanted to. The familiar presence of Anakin was gone, like a disrupted conduit that no longer channeled power the way it was meant to. Ahsoka couldn't feel him anymore, or any of the others. Even the sense of the Jedi as a whole was gone, and she'd been able to feel that since she was too small to articulate what it was that she felt.-Ahsoka
Originally posted by Eli Vanto
You reckon that's what Mace was getting at when he said "Our ability to use the Force has diminished"?
yes. the Dark Side had clouded their ability to see the future which is why Yoda says they should keep it under wraps because only Sidious would've known about the massive shift in the Force