Is normal to lose hair 6 months after hair transplant?

Hello, that sounds like shock loss. Shock loss is due to the loss of normal hair whether it is from donor site or recipient area.  It can occur with both FUE and strip procedures.  Usually if it occurs it will take place in the recipient area.  
Shock loss from hair transplant can occur due to the following:
Anesthesia-  excessively long procedures taking longer than 12 hours can induce shock loss more likely.  the repeated use of lidocaine, marcaine, and perhaps most importantly epinephrine can affect nourishment of the hair
Traumatic harvest-  In strip surgery, traumatic harvest can induce shock loss.  
Recipient area trauma- during the incision making process the hairs are either crushed or cut and damaged during the process.
Ways to minimize shock loss are as follows:
Improve recipient bed and donor area environment.  Make your recipient environment improved by addition of growth factors and/or PRP to help reduce incidence of shock loss to native hairs.
Use of Rogaine and Propecia- can help miniaturized hair become more stable and less likely to fall out during procedure
9xRobotArtas-  The latest version of the robot can make recipient sites and can determine angle of existing hair and help ensure that the angle will not damage existing hair.  Especially helpful in patients where you are transplanting hair to create density
Minimize anesthesia time and procedure time- We limit number of grafts to a safe number per session.  Extended anesthesia periods and harvest times can cause patients to have a higher chance of shock loss.  The 9x Robot harvests between 1000-1500 grafts per hour making it superior to previous additions and traditional FUE approaches.
Best, 
Anil Shah

If you are having issues after surgery, especially with "hairloss" you should contact your doctor.  It is normal to lose 100+ hairs a day.

It is not unusual to lose up to 50 hairs per day due to the normal growth cycle.This may also represent the progression of Androgenetic Alopecia.Finasteride and/or Minoxidil may help with this.