Several problems for 11-staves x 67 bars partiture for choir and quintett, composed in noteworthy editor

Dear Support,
first of all congratulation for this open source software that also runs on android tablets, and thank you for your efforts.
I am trying to use MuseScore for conducting a performance with 11 staves for choir and quintett,
I wrote the original partiture using "noteworthy editor": I am using it since several years and am used to it. However I recently received a large android tablet and would like to try use it instead of paper.

I therefore exported from noteworthy and then transformed it in musicxml using the niversoft online converter https://www.niversoft.com/products/xml2nwc

The partiture has 67 bars, and the choir is not singing all the time. As any partiture, in the original noteworthy file I have the following Flow direction symbols: "Segno", "Coda", "Dal Segno a Coda".

I do not know if as consequence of the conversion or as feature of MuseScore, however, I get the following problems:

a) staves do not run smoothly
I noticed that if a stave on a page does not have lyrics, then the distance between the staves decreases.
Unfortunately I could not find what to do in order to keep the distance constant. I eventually tried to put "fake lyrics" consisting of "spaces" however i did not manage inserting it in the breaks..

b) flow directions are lost
unfortunately they do not show up .

I would like to know what to do to figure out if the issues I observe are "bugs" or are results of the export... and how to fix them (or workaround them). Unfortunately due to time reasons, I do not have the time to re-type the whole partiture in Musescore...

Thank you for your help