2.5 is framed based while 2.6 is time based
2.5 could process some SD tv better (MPEG-1/2 video)
If you find a working 2.5 version: load video and edit as you are used to.
I don't have a working Avidemux 2.5.6 any more (switch from Qt4 to Qt5 on ubuntu), so I'm no longer able to test this.
avidemux 2.6 can read and process .ts, Your .ts has issues