Controller reported heading problems associated with a SID.

Narrative

I was training the D-side at Sector 21. Aircraft X departed FLL on the FEALX2 departure. Aircraft was longitudinally in the middle of 2 other aircraft also on the FEALX departure. The R-side climbed Aircraft X and continued working. Neither the R-side nor myself/trainee noticed Aircraft X make a sharp left turn after FEALX (on the boundary of MIA approach). Aircraft should have turned to BKING after FEALX; keeping them in Sector 21. However the aircraft turned north to about a 010 heading into sector 20. The R-side at sector 20 called us requesting the aircraft be turned to the east. Aircraft X never became traffic or lost separation with any other aircraft in sector 21 or 20. Unfortunately this is the NOT the first time this has happened since we have implemented metroplex. When this has happened in the past; most aircraft somehow miss a single fix on the SID and proceed to the LAST fix on the SID. However; the last couple instances the aircraft hits the fix (FEALX) on the MIA approach boundary then goes direct to the first fix after the SID; bypassing three other fixes (BKING; WOLFO; ETECK). Bypassing the other fixes turns them due north into sector 20 and 02; in conflict with arrivals. I'm not sure how it looks to the pilot when loading their flight plan into the FMS and since it is clearly not a single occurrence at this point; I'm not sure what the next step is to resolve the issue.