I've had both shots - Moderna. First shot was no problem. The day after the 2nd shot, I couldn't lift my arm at all - some pain with no strength, plus the arm was swollen all the way down to my hand, was really sore at the injection point and I had a mild fever. The next day, still no ability to lift my arm. I couldn't get dressed using one arm or sleep on it - I had to sleep in my recliner. Third day, my wife called the emergency clinic and they said I needed to move it (difficult to do when I couldn't even lift my arm) or massage the upper arm at the injection point. My wife massaged the arm for a while and then I did it with my other arm for about 3 hours and it was really starting to loosen up. This was on a Saturday. On Monday, I went to the family doc and he said he thought it was caused by the way the nurse inserted the needle and not the vaccine itself. He thought she may have hit a nerve with the needle (she injected very high on my shoulder, unlike the first shot). It gradually got better over time, but it took almost 10 days before I got full use of my arm back again. Everything now is fine. Never had any other complications or issues. People have said that the 2nd shot of Moderna has some difficulties, but I haven't seen anything official about it.
My wife has had her first Pfiser shot and is scheduled to go back next week for the 2nd one. No issues with the first shot.