Tixati v3.36 on Windows 10
Very often after a download is reported by Tixati as complete it turns out a single piece has not been properly moved from the piece cache to the download. After I do a force check the torrent turns out not to be complete. This seems to only happen with multifile torrents and happens more often when the destination folder is set to a different drive from the one holding the piece cache.
This problem has been persistent since the first Tixati (v2.57) I used over 6 years ago. It happens so often that I've created special checking/checked categories so I know which torrents I've force checked and which have passed those tests. And I've had this problem on multiple different PCs with both windows 7 and later windows 10. I've started doing those forced checks in the past cause I kept encountering video files that wouldn't play in completed downloads regularly and found those torrents to be incomplete after doing a check after encountering those unplayable files.
As far as I can tell it's seems to always be the last piece at the end of the penultimate file and the start of the last file meaning two incomplete files, one of which (the last one) misses it's starting header.
Would be very nice if someone would finally be able to fix this issue.

Addition: I've set Tixati to automatically do a check of the files (not hash) after a download is completed. But even after that check succeeds if I manually do a check later it's incomplete.
It's not caused by hardware issues like bad memory as it happens on different computers who have all passed memtest x86+ memory tests and the prime95 CPU burn tests.
These are some of the settings from the 'File Menu' I use in case they are relevant:
File Allocation - Sparse
Move individual files upon completion = Enabled
Redundant hash-check on completion = File

Also note that my 'Piece Cache' drive, Download drive and 'Move on Complete' Drives are different ones.

if you have a torrent where this happens consistently post the magnet link here so the dev can recreate it.
does it happen if you turn off 'Move individual files upon completion = Enabled '?
is it moving the incomplete files to your complete folder?
do you have incomplete files still in your download folder?

> As far as I can tell it's seems to always be the last piece at the end of the penultimate file and the start of the last file meaning two incomplete files, one of which (the last one) misses it's starting header.

That would be extraordinary if true, as for many many builds now Tixati has deliberately prioritized pre-fetching the starts and ends of all files for EXACTLY that reason - to ensure headers are intact and ends of files are also fetched correctly (the stated reason being that many users download while viewing so ends of video files in particular may not always be reached and finished). If you set sequential downloading and ordered file-completion, you will see that the file starts and ends across the whole torrent are ALWAYS prioritized before the sequential downloading (you might want to try setting those download defaults to see if it makes a difference).

It should certainly not be persistently necessary to force check to get a last missing piece. However, note that you can also set Tixati to do a full hash confirmation check pass on the torrent after downloading, which should be the same as doing your forced check. This might at least help automate your issue.

Since the reported behaviour is not consistent with my observation of how Tixati works and the stated intent of the developers explained above, this must be something unique to your setup or configuration. Nothing you have stated (cache file location etc.) should affect that. :/