SD card taking long time to mount?

[wonderings]

I am in the beginning transition phase of moving to a Lenovo laptop (not by choice). Currently I am on a 5K iMac running Big Sur. I generally run of external hard drives that are formatted for Mac only. I need to start transitioning about 1 TB of files over to the new computer, I decided to use an SD card for this. I have a 512 gig Sandisk SD Card. I have loaded a large portion as well as my entire working folder containing all jobs I am in the middle of (around 150 gigs of files for this). Everything worked fine last week, and was even faster working off the SD card then working off the external. I needed to work from home on the weekend so I took the SD card and mounted it on my M1 Max MacBook Pro to get some stuff done. It took a while to mount on my MacBook Pro, had to restart the computer and then it saw it. I did not think anything of it till I came to work this morning where it seemingly would not mount. It seemed to mount after about 20 mins and me running a disk scanner on it as I was thinking something went wrong and I was going to try and attempt to recover the files. I am not sure if the disk scanner eventually forced it to mount somehow or if it was just coincidence. I have 450 gigs of data on the SD card right now, would this be normal for this to take a while to mount? Or is something going wonky with the SD card?