It is most likely the loose dog on the escapement.  Hopefully it is just seized on its pivot.  To access the escapement properly, you will have to park the drawband (there is a little hook in the carriage bed if you look carefully) and remove the carriage from its rails.  If you can possibly avoid doing this, you will save yourself a lot of trouble trying to get the carriage bearings back into position afterwards.  Instead, try turning the machine upside down on a piece of carpet or similar, and working from underneath with a powerful torch (or flashlight if you are in America )  Lubricate the escapement with sewing machine oil and see if you can make the loose dog move.  If it is actually broken (unlikely) then you have real trouble !

Mosa,

I had this issue for 3 machines in my collection.  I used liberal amounts of denatured alcohol and compressed air blow-outs...repeated 2-3 times until the escapement assembly was "whistle clean".  Problem went away.  Added a drop or so of light machine oil after the clean-ups.
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Well, after fiddling with the escapement rack for ten minutes, I think the whole thing flows smoothly and I consider it good.  Job done.  Funny, working on this is a good reminder that I can fix things on my own with guidance, not rely on someone else to always fix things.   Sure, there are specialists who are amazing, but it's good to get under the hood of a mechanical thing to ascertain the issue, maybe try to fix it yourself, maybe stretch abilities and limits.  Thanks again to thetypewriterman and Pete E for your gracious help.
 

That's a beauty.  75 typewriters!  Major jealousy.  It's super fun to work on these and get them running.  I'm a bit worried I'll never stop.   ;)  Thanks again for all of your help.