k6 v0.38.1 is a patch release containing a bugfix!
Threshold sub-metric selectors containing reserved symbols would fail (#2512)
There was a bug in threshold sub-metric selector parsing, which led to errors when users would use specific symbols such as {, } or : as part of their definitions. For instance, thresholds used for sub-metrics with URL Grouping like http_req_duration{name:"http://example.com/${}"} would have led to failures in v0.38.0.
The error messages for invalid metric, sub-metric and threshold definitions were also improved.
Special thanks to @efdknittlfrank, who reported and helped us track down the issue.