When you confirm a withdrawal, the amount plus its fee (a FALKR withdrawal fee, or the maximum network fee) move from Available to Locked until the withdrawal finishes.
When it completes, that fee is charged; with a maximum network fee, only the actual network cost is charged and the unused part returns to Available. If it is rejected or fails, the full locked amount returns to Available. A withdrawal that needs further checks keeps its reservation until the review ends.
Funds can also be locked as margin in an open Futures position, or while an internal transfer is reserved for review. They return to Available when the position closes or the review ends.
If a credited deposit has to be re-verified on the blockchain, your account is put on hold and withdrawals are unavailable until the review completes; Wallet shows a notice while this happens. Contact support if a locked amount doesn't match anything in your history.