What can I do to make my videos upload to Photos on my mac again?

MyPhotoStream does not transfer video (including the video portion of Live Photos) as documented - for video (and live photos) you have to use USB import or iCloud Photo Library

How to use My Photo Stream - Apple Support

Which photo formats can I use with My Photo Stream?

My Photo Stream supports JPEG, TIFF, PNG, and most RAW photo formats. My Photo Stream doesn't support video or Live Photos.

LN

I import it with a USB connection, but My Photo Stream shows up without connecting my phone to my laptop with a USB.

That is abad mixture, if you are taking Live Photos. The problem is, that My Photo stream will only transfer the still frames of the Live Photos, and when you later try to import them by USB, they will be broken, because the video component cannot be paired with the still fame already in the library.

We still are in the dark about the system versions on your iPhone and Mac. Are you running iOS 11 on your iPhone? Then your iPhone may now be using a new video format and your Mac needs to be upgraded to High Sierra to be using this format, see this document how to adjust the settings on the iPhone and which system versions you need: Using HEIF or HEVC media on Apple devices - Apple Support

How are you importing the videos from your iPhone to your Mac? With a USB connection? With iCloud Photo Library or My Photo Stream? Where is your Photos Library stored? If the library is on an external drive, what is the format of the File system?

Are you seeing any error messages? If yes, what is the error message?

What version of the OS and of IOS do you have? How are you uploading or importing? What ahs changed since it worked?

LN