Andrii, this is a bug in the buildbucket module, not Milo. It should have copied buildsets over to the triggered build. Builder builds have buildset, Tester builds do not. If they did, Milo would render them (unless there is another bug).

I am actually not sure why this is happening. Buildbucket seems to copy buildset tag
https://cs.chromium.org/chromium/infra/recipes-py/recipe_modules/buildbucket/api.py?l=35
but I am not sure what is self.properties there... this needs investigation.

not removing milo component in case there is a bug in milo too

It's a MILO bug. From the tester build I linked to above, here is a copy of buildbucket property which contains buildset as expected:

{"build": {"bucket": "luci.chromium.ci", "created_by": "user:chromium-ci-builder@chops-service-accounts.iam.gserviceaccount.com", "created_ts": 1510716972704100, "id": "8962892155587783088", "tags": ["builder:Linux Tests SANDBOX",

"buildset:commit/gitiles/chromium.googlesource.com/chromium/src/+/33bf8a94dcd5e0abbdf83e4afaed24b5180e3eb2",

"parent_buildername:Linux Builder SANDBOX", "parent_buildnumber:871", "user_agent:recipe"]}, "hostname": "cr-buildbucket.appspot.com"}


I temporarily resolved it by setting 'revision' property, such that latest builds are processed by MILO.

Is anyone taking a look at the Milo bug? 

Not buildbot related so removing UI blocker labels. (still needed for M4 though)

Moved to afterglow