Hi, I have the same problem. I have created a clean erpNext site, which I tested and works fine. I look at the chart of accounts and I can add/edit etc new accounts etc. However, as soon as I import my sql file from production it loads correctly, all the files/accounts are there, but the option to edit or add Child is missing. Were you able to resolve this issue? My production site also does not allow me to edit or add child values?
After a few weeks at that moment, i upgraded the frappe & erpnext (currently, i am still using ERPNext: v8.0.50 & Frappe Framework: v8.0.68), then the chart of accounts is worked again. I do not follow up any more, just consider as a old version with this mirror issue.
For my experience, we need have a development site of frappe & erpnext, upgrade to your specific version, import your data and test them. If everything ok, you can upgrade your production site of frappe & erpnext.
I’m using version 10.1.2. The problem exists if you import the SQL backup to a clean install of erpNEXT. I was on version 8.0 and earlier versions and have continued to update as releases are available. I have not found anyway to fix the issue. I will try importing each record rather than the entire SQL file, but expect this will be tedious and miss some history (like emails sent and notes etc). When I get time I will look at code to see what may be causing this. Stay on ver 8 or try to upgrade later - I would be interested to see if it works for your site.