Captures not uploading to activity feed.

It's not related to the update.

The Xbox console has only a limited amount of reserved space for captures, so if that limit is reached, new captures will "push out" older captures.

If you wish to keep certain captures permanently, you need to use Upload Studio to upload your captures to OneDrive for example.

Then why is it that when i went to look at the recent captures that ive made over the last few days, the only captures i have were from over a year ago?? Where are all of my recent captures? Even the captures i had posted to my activity feed are gone

Screenshots and clips use a limited reserved disc space to save to your console, not the whole capacity of the console disc drive. Once the limit is reached any new shots or clips will overwrite the oldest captures on the console. Upload any captures you wish to keep to the Xbox network and/or to Onedrive. From there you can share to Activity feed, Clubs etc.

What you need to do is copy your captures to the captures folder on Windows 10, should be in your videos folder. Then launch the Xbox app, select captures, then select this pc, and your captures should be listed, select the capture you want to upload, and
give it a name, and choose the game it's for, and select upload. Once it is uploaded it will take a few hours to go on the xbox live feed.

Actually, with the Xbox App on a PC you can download or UPLOAD captures to your feed.

Is auto upload clips enabled because if not then it will result in it not posting in the activity feed.

Settings - preferences - activity feed - share clips & screenshots automatically.