Is the Pinch in my Arm a Normal Side Effect of Liposuction?

After 4 months most dysthesthesias tend to resolve. If this has not dissipated within the next two months, it could represent a neuroma which may require excision. This would be exceptionally rare.
Massaging the area vigorously 3 times a day for the next three weeks may produce improvement or at least desensitization of the area. You may want to seek evaluation by your surgeon as well and discuss your symptoms.

A pinching feeling after liposuction even several months after the procedure may be the result of some scar tissue.

It is common to have small pinches that last a few seconds and then go away for months after liposuction. This is due to nerve endings which were bruised during surgery. Nerves grow very slowly. You can expect this will gradually resolve on its own after a few more weeks as the nerve ending continues to grow and heal. Hope this helps.

After liposuction, little nerves can be bruised, and they cause strange sensations while they are healing.  It will go away in a few months.