When creating an application based on devfile "Import from Git" in Developer console using only GitLab repo, the following error block to create it.
It only happened when using GitLab, not Github. And CLI operation based on "oc new-app" could work well. In other words, the issue is only for Dev console.  

  Could not fetch kubernetes resource "/deploy.yaml" for component "kubernetes-deploy" from Git repository https://{gitlaburl}.

4.15.z

Always

You can always reproduce according to the following procedures.
a. Switch "Developer" mode at your web console.
b. Move "+Add", then click "Import from Git" in "Git Repository" section at the page.
c. Input "https://<GITLAB HOSTNAME>/XXXX/devfile-sample-go-basic.git" to the "Git Repo URL" text box.
d. Select "GitLab" at "Git type" drop box.
e. You can see the below error messages.

The "/deploy.yaml" file path evaluated as invalid one with 400 response status during the process as follows.
Look at the URL, "/%2Fdeploy.yaml" shows us leading slash was duplicated there.

  Request URL:
    https://<GITLAB HOSTNAME>/api/v4/projects/yyyy/repository/files/%2Fdeploy.yaml/raw?ref=main
  Response:
    {"error":"file_path should be a valid file path"}

 The request URL for handling "deploy.yaml" file should be removed the duplicated leading slash and provide correct file path.

 Request URL:
   https://<GITLAB HOSTNAME>/api/v4/projects/yyyy/repository/files/deploy.yaml/raw?ref=main
 Response:
   "deploy.yaml" contents.

I submitted a pull request to fix this here: https://github.com/openshift/console/pull/13812