I have a strange problem that the torch tool stopped or stuck after few seconds in version 5.26, any idea please?

This is happening for me too under 5.25 on an RB1100AHx2.

When starting Torch on any interface, it does not detect any traffic whatsoever.
I reboot the unit through Winbox, then reconnect and start Torch again (with all default settings) and now it detects traffic.

Actual network traffic is not affected despite Torch showing "no traffic" flowing through the interface.