I submitted a manuscript to a journal in the social sciences. The response to the initial submission was "accepted with conditions". The only feedback I received related to a few typos and grammatical errors. I reviewed the entire paper for additional typos, made some minor edits to improve overall flow, and resubmitted the manuscript. Four months later, I received a letter indicating that the manuscript "can be publishable with major revisions". To me, this decision sounds like the manuscript is farther from being accepted for publication than it was after the initial "accepted with conditions". Am I interpreting the journal's decision correctly?
The solution -- as in so many cases in life -- is to communicate. In this case, write to the editor in charge and ask what happened here and how they intend you to proceed. Like @Buffy mentions, it is likely that the second round of the paper went to different reviewers. This is not entirely uncommon, but awkward anyway -- the editor should have looked for substantive reviews the first time around already, rather than just go with the typo fixes. But it happens, among other reasons because a reviewer who promised a review just doesn't get it done, and the editor feels the need to go with what they have -- just to receive the missing review a week later.
It is likely that your paper got sent to a different reviewer (or several) who had different ideas bout the paper. I don't think your changes are to blame here, but I hope you are getting guidance as to the nature of the requested revisions.
I don't think this is entirely uncommon.