Cannot amend any customer records (even when logged in as SA etc..)
You may have a status on your customer lifecycle which states that the "Customer" status is read only = true. From 721 the lifecycle is now correctly setting the record to read only at this point.
Assuming that you do need to amend customer records at this stage in your customer lifecycle you need to change the read only flag to false. You can't change this flag through the console once the status is in use so can do via the db (I found that I needed to run an IIS reset too):
Update lc_status set lc_is_readonly = 0 where lc_name = 'Customer'
before running this statement on your live environment please test on your test environment and also ensure that you take a full backup prior to applying this fix.