unable to view existing MR

Gitlab CE 12.3.4

I did a brief update to 12.5.0 before rolling back again due to other issues. Newly created ones seems to work, so I don't know what conditions are actually needed to reproduce this. Thank you

NoMethodError (undefined method `storage_name' for nil:NilClass):

lib/gitlab/gitaly_client/util.rb:23:in `git_repository'
lib/gitlab/gitaly_client/conflict_files_stitcher.rb:34:in `file_from_gitaly_header'
lib/gitlab/gitaly_client/conflict_files_stitcher.rb:20:in `block (2 levels) in each'
lib/gitlab/gitaly_client/conflict_files_stitcher.rb:16:in `each'
lib/gitlab/gitaly_client/conflict_files_stitcher.rb:16:in `block in each'
lib/gitlab/gitaly_client/conflict_files_stitcher.rb:15:in `each'
lib/gitlab/gitaly_client/conflict_files_stitcher.rb:15:in `each'
lib/gitlab/gitaly_client/conflicts_service.rb:29:in `any?'
lib/gitlab/gitaly_client/conflicts_service.rb:29:in `conflicts?'
lib/gitlab/git/repository.rb:981:in `can_be_merged?'
app/models/repository.rb:478:in `method_missing'
lib/gitlab/metrics/instrumentation.rb:161:in `block in method_missing'
lib/gitlab/metrics/method_call.rb:36:in `measure'
lib/gitlab/metrics/instrumentation.rb:161:in `method_missing'
app/services/merge_requests/mergeability_check_service.rb:141:in `can_git_merge?'
lib/gitlab/metrics/instrumentation.rb:161:in `block in can_git_merge?'
lib/gitlab/metrics/method_call.rb:36:in `measure'
lib/gitlab/metrics/instrumentation.rb:161:in `can_git_merge?'
app/services/merge_requests/mergeability_check_service.rb:113:in `update_merge_status'
lib/gitlab/metrics/instrumentation.rb:161:in `block in update_merge_status'
lib/gitlab/metrics/method_call.rb:36:in `measure'
lib/gitlab/metrics/instrumentation.rb:161:in `update_merge_status'
app/services/merge_requests/mergeability_check_service.rb:55:in `check_mergeability'
lib/gitlab/metrics/instrumentation.rb:161:in `block in check_mergeability'
lib/gitlab/metrics/method_call.rb:36:in `measure'
lib/gitlab/metrics/instrumentation.rb:161:in `check_mergeability'
app/services/merge_requests/mergeability_check_service.rb:43:in `block in execute'
lib/gitlab/exclusive_lease_helpers.rb:29:in `in_lock'
app/services/merge_requests/mergeability_check_service.rb:85:in `in_write_lock'
lib/gitlab/metrics/instrumentation.rb:161:in `block in in_write_lock'
lib/gitlab/metrics/method_call.rb:36:in `measure'
lib/gitlab/metrics/instrumentation.rb:161:in `in_write_lock'
app/services/merge_requests/mergeability_check_service.rb:37:in `execute'
lib/gitlab/metrics/instrumentation.rb:161:in `block in execute'
lib/gitlab/metrics/method_call.rb:36:in `measure'
lib/gitlab/metrics/instrumentation.rb:161:in `execute'
app/models/merge_request.rb:755:in `check_mergeability'
lib/gitlab/metrics/instrumentation.rb:161:in `block in check_mergeability'
lib/gitlab/metrics/method_call.rb:36:in `measure'
lib/gitlab/metrics/instrumentation.rb:161:in `check_mergeability'
app/controllers/projects/merge_requests_controller.rb:37:in `show'
app/controllers/application_controller.rb:533:in `block in allow_gitaly_ref_name_caching'
lib/gitlab/gitaly_client.rb:300:in `allow_ref_name_caching'
app/controllers/application_controller.rb:532:in `allow_gitaly_ref_name_caching'
lib/gitlab/session.rb:11:in `with_session'
app/controllers/application_controller.rb:450:in `set_session_storage'
lib/gitlab/i18n.rb:55:in `with_locale'
lib/gitlab/i18n.rb:61:in `with_user_locale'
app/controllers/application_controller.rb:444:in `set_locale'
lib/gitlab/middleware/rails_queue_duration.rb:27:in `call'
lib/gitlab/metrics/rack_middleware.rb:17:in `block in call'
lib/gitlab/metrics/transaction.rb:57:in `run'
lib/gitlab/metrics/rack_middleware.rb:17:in `call'
lib/gitlab/request_profiler/middleware.rb:17:in `call'
lib/gitlab/middleware/go.rb:20:in `call'
lib/gitlab/etag_caching/middleware.rb:13:in `call'
lib/gitlab/middleware/correlation_id.rb:16:in `block in call'
lib/gitlab/middleware/correlation_id.rb:15:in `call'
lib/gitlab/middleware/multipart.rb:117:in `call'
lib/gitlab/middleware/read_only/controller.rb:42:in `call'
lib/gitlab/middleware/read_only.rb:18:in `call'
lib/gitlab/middleware/basic_health_check.rb:25:in `call'
lib/gitlab/request_context.rb:26:in `call'
lib/gitlab/metrics/requests_rack_middleware.rb:29:in `call'
lib/gitlab/middleware/release_env.rb:12:in `call'