I don't think that the antenna trace causes particular problems. Most serious problem is most likely having too few ground vias, also probably ground plane discontinuity. We need to see the full design.
Another question is if the said interferences are possibly observed with a GSM antenna near to the board. If so did you try to displace it to a distant position?
In regards to the antenna trace, I just want to make sure everyone understands the attached design is how I want to do it in future... below is the current layout that is giving me problems.
*Bottom ground plane not shown
As requested, here is the full design:
To understand why I have mentioned that it must be something related to the board design, specifically the antenna, I need to show some pictures:
In the first photo, everything works perfectly. In the others, the micro freezes up every time it transmits on the GSM network.
Regarding your last suggestion, I have moved the antenna far away by using a pigtail and an external antenna located a good 1.5m away from the board. This gave me both better signal and made the problem worse. With the external antenna I need to orient the connector to a certain rotation, and pull the pigtail straight up vertically away from the board to ensure the micro does not freeze up.
Also, it is not a power supply related problem. Have analyzed it extensively throughout using an oscilloscope.