Suddenly started getting 500 on all endpoints OPTIONS requests


I have a project that is set up on one AWS Lambda function running express.js through aws-serverless-express.
I’ve had perfectly working Continuos Deployment on GitLab, but one day it suddenly stopped working as expected: After deployment, OPTIONS request on every endpoint gets 500 response code.
I’ve noticed, that when I deploy the project from my local machine (it is done simply with serverless deploy commad) everything works correctly and there’s no 500 error.
Recently deployments from my local machine have stopped working as well. I cannot find the issue.