Hi @anandreum, @marpet,
Unfortunately I didn't solve the problem. I have updated SNAP at the last version on my ubuntu Virtual Machine nevertheless the issue persists. Moreover I have realized some other strange things that could be useful to know.
The screen below shows an SL_2_LST product (acquired today) opened in SNAP 6.0 on Ubuntu. The land surface temperature (LST) should be under Bands but it is under Tie-Point Grids. The same assumption is valid for the other data such as NDVI, TCWV etc. Moreover as reported by @abruescas the showed scene is narrower than expected.
On the contrary here below there is the same product opened with SNAP on Windows OS. LST and the other data are correctly listed under Bands and the covered scene is the expected one.
Basically it seems that on Ubuntu information are switched, e.g. bands with tie-point grids (please have a look at the screens below) and so incorrectly visualized. Therefore Masks are missing. Same issues are observed using the snappy python plugin.
Tie points grid in Windows:
Tie point grids under Bands in Ubuntu: