Hello Dominique
Sometimes GNS3 can behave in this way. It does occasionally occur where some behaviour is strange, but a reboot or a restart of the lab brings about the expected results. Sometimes it just “gets stuck”. It’s one of the quirks of GNS3 that we have to live with 
SRLG is indeed an important feature of MPLS as seen below.
https://www.cisco.com/c/en/us/td/docs/ios/12_0s/feature/guide/fs29srlg.html#wp1027195
However, SRLG is also a parameter that can be configured on the interface itself. In some IOS versions, the command is implemented differently. There is an srlg configuration mode under which the participating interfaces can be indicated and values can be configured. This of course is for another IOS version specifically for CRS routers, but you can take a look and see if your IOS version will allow these commands.
I can get Rene to take a look and share which IOS version he is using in his lessons to verify the commands.
I hope this has been helpful!
Laz