Why are fingers tingly four months after endoscopic carpal tunnel release?

Numbness CTR. Depending on the severity, carpal tunnel syndrome after skilled surgery can take up to 6 months to improve. If the night pain has improved, but the numbing and tingling has not fully resolved, you can still be part of the >90% that get better with time. You are 2/3 the way there! the blood supply improves immediately, and with it the pain. The insulation (myelin) takes time, so it can take months.
Severe disease. Depending on the severity of your carpal tunnel disease normal feeling may not return after carpal tunnel release. Additionally you may have other underlying causes for neuropathy such as diabetes, thyroid disease, cervical spine disease or nutritional deficiencies. In some cases, an endoscopic release may not be adequate. You may need an open procedure. You should follow up with your surgeon and discuss with him or her.
Severity . The more severe the compression on the nerve before surgery can delay the return to normal function by months even up to a year. Sometimes the damage done to the nerve has been permanent so despite carpal tunnel surgery to relief the pressure, the nerve may never regain full function. Other factors should also be treated such as diabetes and hypothyroidism to minimize any neuropathy issues.