Barlines not connected in Classical and Symphonic orchestra scores.
Using OS: Windows 10 (10.0), Arch.: x86_64, MuseScore version (64-bit): 18.104.22.1689883548, revision: github-musescore-musescore- (last nightly created as of this time).
When you open the instrument dialog and apply Orchestra ordering to a score or create a score from the Classical orchestra or **Symphonic orchestra templates (which default to Orchestra ordering), the barlines on the strings do not connect like they do in other sections (woodwinds, brass and percussion I haven't tested choral parts). Creating a string orchestra or string quartet the lines are connected. It seems that solo instruments (Violin, Viola...) are connected while string sections (Violins, Violas...) are not connected.
* Note 1: This applies to some scores. The details for determining which ones these apply to are still being investigated. It is possible the instruments not connecting barlines are from the ASO instrument list.
** Note 2: On the symphonic orchestra it seems that only the violins do not connect barlines while violas, cellos & basses do.