I would say that the bearings are binding and need to be cleaned of the packing grease and then lubricated with a good oil.

There are many oils that can be used though many you may already have in your home.
Spray oils include WD40, Spray Silicone Garage Door lubricant and good old Ballistol Oil-Lube Cleaner 4oz Non-Aerosol.
If you clean a new linear bearing you will find that it is packed with so much crud I would never use on without first cleaning with a de-greaser.
Then oiling it with your choice of lubricants.

I have seen where some have used a grease, I tried and found it only made the 3D Printers steppers miss steps because too sticky.

Could also be that the 3D Printer is not aligned correctly and binding between the smooth rods an the bearings.