OT: Vim masks (hides) multiple lines with a comment

[Anton Shterenlikht]

This is an OT question, on Vim in general.
(This is on linux, not FreeBSD, where there is no nvi, just Vim.)

Sometimes Vim would mask some lines of text like this:

 55 **!***********************************************************************
 56 *DEPVAR, delete=15
 57 +-- 19 lines: 18--------------------------------------------------------------------------------
 76 ** ALL ZERO initially, EXCEPT 15
 77 *INITIAL CONDITIONS,TYpe=SOLUTION
 78 +--  3 lines: ALL, 0, 0, 0, 0, 0, 0, 0----------------------------------------------------------
 81 **
 82 ** >>>>> END   OF USER MATERIAL PART <<<<<<
 83 **

I cannot find a setting or a command to
unblock the hidden lines. The only workaround
I know is to launch Vim as "ex -v".

If I go into the edit mode on hidden lines,
then they are unmasked, but this is not an
acceptable workaround, as I don't want to
edit, just see and check.

I searched online multiple times but cannot
see anything relevant. Maybe my search phrase
is not right.

Please advise

Thanks

Anton