I have the same issue, with OJS 3.4.0.1 and 3.4.0.5.
I already have a journal where DOIs are working, and have configured another journal for DOI. Looking at Distribution → DOIs (/management/settings/distribution#dois) they have the same configuration, apart from the Crossref credentials.
It looks like the enabledDoiTypes prop of the DoiListPanel Vue component is being set to something that is not quite an Array:
Hope that helps!