If the STMS buffer cleanup automatically after adding transport & you cannot see any TR in STMS_IMPORT screen and the buffer file shows :
#1/_TASK CLITRELESAPUSER EXL W H A I r0 C r1 0 V R G < K T t r5 umodes ASCL20130828182513000 00000PROJECT P033 A # buffer cleaned on 20160824182513
You can also find the same thing in TP log. it shows cleanup run in last.
Please cross check that all systems in STMS Path should be on same transport group – (GROUP_SID). Change the same & redistribute it.