I have found two instances of a single consonant having two vowels attached to it. These are Lam 3:25 לְקוָֹ֔ו and Isaiah 49:23 קוָֹֽי. Are these errors in coding or is there some other significance?
These are/were errors in coding in the popular tanach.us versions of WLC that appear in various places on the Interent (and even in a few places on paper!). Or, perhaps better-put, they were errors in transcoding, i.e. errors in moving from one encoding system (Michigan-Claremont) to another (Unicode). These errors were fixed in the October 2020 release of UXLC, a few months after you made your post about them here.
These are/were errors in coding in the popular tanach.us versions of WLC that appear in various places on the Interent (and even in a few places on paper!). Or, perhaps better-put, they were errors in transcoding, i.e. errors in moving from one encoding system (Michigan-Claremont) to another (Unicode). These errors were fixed in the October 2020 release of UXLC, a few months after you made your post about them here.
Isa 49:23.20 change (tanach.us)
Lam 3:25.3 change (tanach.us)
As to true diphthongs, like ḥolam-yod and shuruq-yod... we can discuss those another day!