Error: File to import not found or unreadable: bootstrap/scss/variables after Upgrading from 3.3.7 to 3.4.1

[akashp-18]

Received a notification from BOT: [Security] Bump bootstrap-sass from 3.3.7 to 3.4.1 Commit

After merging the same I am receiving Error: File to import not found or unreadable: bootstrap/variables

I am importing
@import 'bootstrap/variables'; @import 'bootstrap/mixins';
in my rails view file (_colors.scss.erb) Which seems to create the above issue on Heroku.
Rails Version : 4.2.10
Ruby Version: 2.5.5

Looks like it is not able to locate file _variables.scss present in node_modules/bootstrap/scss. After giving the relative URL also it was giving same issue.

Tried solution suggested on https://stackoverflow.com/questions/48434762/error-file-to-import-not-found-or-unreadable-bootstrap-scss-bootstrap But it did not help.

Any help will be appreciated.

[fang-niuwa]

have you restart rails server after importing those modules?