A number of times Ive noticed torrents are not fully downloading even thoygh its treated as completed. I notice this happens when I resume torrents

Usually that means someone included system metadata files (like thumbnails) in the torrent, and your graphical environment has written its own data into them. New files don't match the data torrent client needs to exchange with others, so they are re-downloaded. Or you have cracks and other types of files system antivirus considers unwanted. Maybe it's time to learn how to control it, check its activity in logs, figure out whether removed files were legit, or actual viruses (can easily happen if you download crap from internet without thinking for even 5 seconds), change the settings to prevent such problems.

You can always stop the torrent, do a manual re-check, and see which files are missing, then start figuring out why.

I've also seen cheap HDD's behave like this where the download completes OK at 100%
But if you force recheck, the download will be at 99% as one piece has later failed its hash-check.

That's why it's important for all download clients to 'recheck on completion'

You could investigate HDD and memory checking tools and leave running overnight to identify or eliminate that problem.

Having said that, somebody on here recently was "keeping notes" inside the download files
That would cause a hash fail as the file isn't as per the original anymore.

Ok ta

Whats the difference btw redundant hash check on completion of file and the other option, transfers

Assuming that it does what it says on the cover…

File data in each torrent is split into fragments (“pieces”). Each one has its hash listed on creation of metadata file. After getting each complete piece from one or many peers, clients check that the hash matches, then save the data into corresponding files. Naturally, if you've checked each piece, you know that the whole thing is correct after it finishes, and have no need in checking any data redundantly.

Unfortunately, other programs running in a multitasking system may do something with those files, too. It can be a music player scanning the database, and updating something in audio file tags, it can be an antivirus tool reacting to suspicious fingerprints or features it thinks it sees in files. The latter usually breaks correct data processing in other programs when it modifies or removes files, and manipulate file access requests. So you have the option to check each file after it is written to disk, or check all of them when everything is already written, and react to possible errors immediately instead of finding that something is broken when it's too late.

To be more specific, Windows Defender is the thing from which this option protects you. It is inconvenient to manage, and regular people usually are not taught how to do it anyway (the reason for that is not just “the safety of technically illiterate”, but also Defender being important data collection and system control tool for Microsoft). Still, I believe it's your job to set the system properly, and make sure that nothing corrupts your files before storing them.