I feel your pain, Peg.
From what I can tell, Xmarks will always be LastPass' perennial red-headed stepchild. Which is sad, since before being purchased by LastPass, Xmarks was that 'godsend'.
I have been heavily using LastPass & Xmarks for a couple of years now. Most recently, I've been test-driving LastPass Family. But I have started looking at alternatives, in large part because of the lack of active development & support for Xmarks. The pain threshold for changing has been met with the issues related to Firefox 57.
Peg, for flawless bookmark synchronization, consider looking at the publisher-specific solutions. Both Google & Mozilla have very good, very stable sync features. These can also be used for passwords, if you so choose. Of course, that leads to a new kind of product lock-in. However, both Google & Mozilla have comparatively excellent track record with making sure their sync utilities "just work."
Google Chrome's sync is explained here - https://support.google.com/chromebook/a ... 4794?hl=en
Mozilla Firefox's sync is explained here - https://support.mozilla.org/en-US/kb/ho ... y-computer
By the way, I have also had a very good experience with mobile Firefox. Best of luck, Peg. I'll monitor this thread if you happen back and want to continue this convo.