2010 RX350.
Windshield vipers replaced. However, the driver's side wiper is moving in a "jittery" fashion - i.e. not gliding smoothly across the windshield. This is particularly visible on the bottom part of the wiper.
What could be causing that?

 

Could be a product defect or an improper installation. What was replaced? Just the wiper blade refills? The entire assembly? Go back to the installer, explain the issue, and have them check it out. They should not charge you for investigating the problem.

 

Not uncommon with the longer blades.

 

Rubber wipers are the cause of that. You should return your new wipers and get some silicone ones, and that will fix your problem.
If you can't return your blades, try using some windshield sealant, like Rain-X it sometimes helps

 

You should first really clean your windshield as dirt & environmental buildup is probably the main reason new blades will do that. I recommend cleaning it with Glass Science Glass Scrub then treating the windshield with Glass Science Rain Clear. They are later generation products made by the guy who invented Rain-X and then sold the company. You can probably find them at Amazon or Car Detailing sites online.
https://glassscience.com/