Channel Angle connection

Hello,

I am performing simple staad analysis and I am getting instability at one of the middle member. Can someone help me to rectify it, please? As per my understanding releases in staad are local and not global so I have released MY and MZ in the middle angle which is facing instability in direction MX and I can't release MX as it would cause torsion then.

STAAD SPACE
START JOB INFORMATION
ENGINEER DATE 08-Feb-18
END JOB INFORMATION
INPUT WIDTH 79
UNIT FEET KIP
JOINT COORDINATES
1 0 0 -2.5; 2 6.5 0 -2.5; 3 0 0 -3; 4 6.5 0 -3; 5 3.25 0 -2.5; 6 3.25 0 -3;
MEMBER INCIDENCES
1 1 5; 2 3 6; 4 6 4; 5 5 2; 6 6 5;
DEFINE MATERIAL START
ISOTROPIC STEEL
E 4.176e+006
POISSON 0.3
DENSITY 0.489024
ALPHA 6e-006
DAMP 0.03
TYPE STEEL
STRENGTH FY 5184 FU 8352 RY 1.5 RT 1.2
G 1.60615e+006
END DEFINE MATERIAL
MEMBER PROPERTY AMERICAN
1 2 4 5 TABLE ST C4X6
6 TABLE ST L30208
CONSTANTS
BETA 180 MEMB 2 4
MATERIAL STEEL ALL
SUPPORTS
1 TO 4 PINNED
MEMBER RELEASE
6 START MY MZ
6 END MY MZ
LOAD 1 LOADTYPE Dead TITLE LOAD CASE 1
SELFWEIGHT Y -1 
JOINT LOAD
1 3 FY -1
MEMBER LOAD
1 2 CON GY -1 2
4 5 CON GY -1 0.75
4 5 CON GY -0.8 2.75
LOAD 2 LOADTYPE Dead TITLE LOAD CASE 2
SELFWEIGHT Y -1 
JOINT LOAD
1 3 FY -0.2
MEMBER LOAD
1 2 CON GY -0.1 2
4 5 CON GY -0.1 0.75
4 5 CON GY -0.1 2.75
JOINT LOAD
1 3 MX 2.25
MEMBER LOAD
1 2 CMOM GX 0.75 2
4 5 CMOM GX 0.75 0.75
4 5 CMOM GX 0.05 2.75
LOAD 3 LOADTYPE Dead TITLE LOAD CASE 3
SELFWEIGHT Y -1 
JOINT LOAD
1 3 FY -0.2
MEMBER LOAD
1 2 CON GY -0.1 2
4 5 CON GY -0.1 0.75
4 5 CON GY -0.1 2.75
JOINT LOAD
1 3 MZ 1.5
MEMBER LOAD
1 2 CMOM GZ 0.75 2
4 5 CMOM GZ 0.75 0.75
4 5 CMOM GZ 0.25 2.75
PERFORM ANALYSIS
PARAMETER 1
CODE AISC UNIFIED 2010
FU 8352 ALL
FYLD 5184 ALL
UNT 0 MEMB 6
METHOD ASD
CHECK CODE ALL
FINISH