Sounds like Pcloud is continually remounting the drive, causing LR to get notified of a "new" drive and opening the Import window. Over the years there have been a fair number of reports about similar situations (background services remapping drive letters, loose cables, etc.).
Sameer's suggestion of disabling Show Import Dialog When A Memory Card Is Detected will stop the Import window from opening. But if you want Import to open automatically when you insert an SD card, you'll have to contact Pcloud support to see why their service is continually remounting their drive.