Just found and fixed a dropout problem, maybe this will be useful to other folks.
 
I hadn't booted the DAW in a long time, like many months.  I just did recently and brought up one of the last projects I was working on.  Hit play and several seconds into it 6 acoustic guitar tracks started dropping out for about a second every several seconds.  Turns out I had an instance of iZotope RX 3 on each of those tracks (tracked open mike in a room with computer fans running).  If I turned off RX3 the dropouts disappeared.  When I went to open the RX3 dialog on one of the tracks I was prompted to authorize the software, which I did, and that fixed the dropouts on all of those tracks.  Although the software had been authorized many months ago, apparently the lack of use or some other factor somehow deauthorized it.  Weird but true.

when ever someone mentions they have no signal on 1 track, I typically always suggest they check routing, plugins or mute. but you are right, its funny how little thing like this will stump you and it turns out to be something strange like that.
good post.

Seems like every time Windows 10 gets an update I have to reauthorize a few plugins.

I concur on the above post with Windows 10 updates sometimes making it so that some software needs reauthorization.  No idea why.
 
Bob Bone