Why faster on short swim sets?

Or do more than 10 of them. A lot more.

Has your stroke changed any since you posted a video last year ?  At the paces you are swimming a years a long time to go without any gains.  Have you worked on anything with your catch for starters ?  If you have just been doing the same thing for the last twelve months I'd say go back and read the suggestions in those threads.  There were some good tips in there.

If you have been working on it I'd see if you can get someone to record you again so we can take a look at what's going on. 

The intervals tab looks OK - not sure about the hover data issue.

Looking at your data, 16-17 strokes (which is really 32-34 because your Garmin only counts one arm) is a LOT to swim one length.  You must have a really quick turnover rate to get across in 30 seconds.  Without looking at video, I would bet it looks like you're really thrashing in the water and not getting any kind of catch and pull.

I'll leave the suggestions to the swim coaches on here, but that data really jumped out at me.

from what I remember of your video I would definitely not at more glide to your stroke.  Among other things you have no real "catch".  Your hands are just moving through the water not pulling you through it.  There's some fundamental flaws.  I also seem to remember you don't really have access to a swim coach.  Try swimsmooth.com for some basics.  The videos might be very helpful to you. 

That's what I was thinking, too.  Hands and arms are just flailing through the water without any energy delivered to move the swimmer forward.

Good work.   You're definitely crossing over with your left arm...it needs to enter the water out wider.  You are also really cutting your stroke short.  Think about brushing your thumb against your thigh.  Check out how far Juno extends his hand on the back half of the stroke...you lose a bit of momentum by cutting your stroke short.  This is something I continually work on too ... my coach is always encouraging me to extend to the hip.

https://www.youtube.com/watch?v=s3HhNlysFDs&feature=youtu.be

A good gauge of how efficient your pull is to count the number of strokes per 25.  Assuming a 25 yard pool, you'd want that number to be below 20 for mid-pace efforts....probably about 22ish for a 25m pool.  It looks like you came in at about 28 for 25m.    Do 2 to 3 sets of 4x25' and try descending your stroke count for each 25.  Something like 28,27,26,25.  Try to get as close to 22 (or better) as you can.  Rinse and repeat.  The focus of this exercise is to get you to concentrate on the mechanics of getting the most out of each stroke.  

I'm even simpler than all the above (correct) advice. 

Your CATCH is clearly lacking. 

Unfortunately, the only way to really improve your catch is to swim a lot, and often harder. In your case (and in most cases) lack of a catch is a muscular endurance situation where you need to have enough physical ability in your arms to execute an effective catch. 

The 'windmilling' of the arms occurs because your body/brain recognizes quickly that you can't sustain the force required to swim, say, a 1:30/100 pace, and thus it will drop the elbow and do other things to keep that arm moving as you want it to. Unfortunately, that means you're decreasing the effectiveness of your catch, and you go slower as a result. 

There a bunch of technical things that can be improved in the stroke, but honestly, the lack of power/muscular endurance is by farrrr the dominant feature. And you're not going to be able to just do a bunch of drills and magically chop of 20sec/100 - it's going to take hard work AND attention to technique. 

I definitely disagree with anyone who will suggest you have the physical capability RIGHT NOW to swim sub 1:40/100m, and that your technique flaws are the sole factor holding you back.