I haven't seen that happening yet. It 'probably' means the file is checking against the original hash it downloaded from to be sure it's 100% correct.

Is it a video file? Video files will take much longer to verify.

As a last resort, you could close LW, check the file in the incomplete folder (perhaps make a copy of it), play or open it & if it's all ok, then remove it from the incomplete folder. Open LW & be sure it's not listed in the download window, if yes, then cancel it.

Though perhaps if it does it for over an hour, then close LW, re-open & see if it eventually finishes.