Certainly. The Sync with External Folder command is intended to allow editing of Scrivener projects with tools other than Scrivener. It is not to be used for synchronization with iOS Scrivener. I made the mistake of linking the Dropbox folder on my computer with Scrivener’s External Folder Sync. This mistake caused my syncing issues. Once I disabled the External Folder Sync everything worked fine.
I’m still firmly committed to plain text. The difference in my approach is that I now understand, as I posted here, that I am able to export/compile from RFT in Scrivener to markdown. I am not locked in. Additionally, I can bulk export or convert RTF files to markdown and/or plain text from many of the programs I’m currently using or I can use DEVONthink to bulk convert my files if a particular app does not have an export to markdown option. An example are my notes in Apple Notes. With the Exporter app or by using DEVONthink, I can bulk convert my Apple Notes to markdown as needed. I have setup a monthly reminder to do just that.
I have the advantages of both RTF and plain text files, I’m not locked into using either. In short, I can have my cake and eat it too. 
PS: I’ll add that one of the nice things about coming to this realization is that I am discovering the convenience of using Apple Note’s Quick Note (QN) and Scan Documents (SD) features. I’m now using QN to compose draft emails that require time and consideration before sending. I’ve always used Drafts for this. I’m now using QN. I draft and finalize the email and when ready, I copy and paste it into Apple Mail and send it. This is nearly as quick as using a Draft Action. The advantage is that I have one less app preloading and running in the background. I still use Drafts for a few things but AN is covering most of what I need. I’m experimenting with using AN’s SD feature to scan receipts and then emailing them to my EA. I have a lot of business meals. I have been using Genius Scan to scan receipts and then emailing them to my EA. Genius Scan is a great app, I have no complaints about the app. But, if AN serves my purpose I again have one less app with which to contend.