It seems that there is a conflict while you attempt to transfer photos from the SD card to your Mac causing the photos to disappear from the SD card. Then, the best choice for you is to perform photo recovery on the SD card to retrieve your lost photos ASAP! Don't continue to use the SD card before recovering!
Given that the available space in your photo library is insufficient, the transferring process should haven't begun or it has been interrupted when the space is used up. As you said, you have clicked delete photos after import as always, you probably cleared those selected photos you want to import from the SD card.
Anyway, the photos should display on your SD card or your Mac, but if you can't find those imported photos anywhere, you can try to recover lost photos on your SD card and the Mac. There are two ways you can choose from.
If you have enabled Time Machine on your Mac and connected the backup drive when the SD card is plugged in, then you may have created a backup of the SD card and your Mac before the photos are missing. If so, insert the Time Machine backup drive into your Mac, and restore photos from it.
In case there is no available backup, then the third-party data recovery software is what you need such as iBoysoft Data Recovery for Mac. It can scan out deleted/lost files on your SD card and make them visible for you, then you can preview the scanned photos and recover the wanted ones to a different location. Free download and have a try!