Swimming activity confuses a change in swim style to be a new lap

Always have had this issue. You need to kerp your stroke for the whole lap. Watch thinks it missed the new lap. It looks for a pause and push off normally. 

for me the weird part is that only switching from crawl to breaststroke causes this.. which is especially bad if you have a slow swimmer in front of you that you want to overtake but have to wait until one person on the other lane passes by

I have had a feature request in with garmin for months to enable manual laps. I use my swim pro to do this same thing. I am healing from some back issues, and I do switch my stroke alot, and swim slower to start. My watch was counting 10 laps in one sometimes. 

That would be one way to solve it but I would hope that they fix the fundamental issue

But for now i think I'll stick to your hint that I just have to keep my stroke for the lap

I am also affected by this. When a slower swimmer is ahead of me, I often switch to *** stroke so that I can see better if it’s safe to overtake.

Here’s a workaround: On my Forerunner 235 I used the “Other” activity type for swimming. Each length of the pool I hit the back button to count a lap. Afterwards, I’d manually enter the pool size and number of lengths in Connect.

i had a similar effect, on a venu with sw 3.50
breaststroke detection seems to break a lot of things. If i swim only ***, nothing is detected. If i swim only crawl, everything is detected
If i start ***, then switch to crawl after 1 or 2 laps, no *** detected. If i start crawl and switch to *** after few laps, everything is detected!