Lidia please can you let us know what softwear you are using?

Sounds like tie-offs. I would test the design as is and then decide. Hugs. Nan

Which software program do you use? It is possible that those might be tie offs. However stitches with 0 length, that aren’t tie offs, put repeat holes and extra thread in your project that you probably don’t want.
You may be able to take a closer look at exactly which stitches the program has identified. Some software has the ability to list each “object” in the design with the # of stitches it contains. Isolate and inspect the object to determine what it is and whether it is truly necessary.
That said, in my own experience, I have been able to eliminate those excess stitches without any consequence to the design.
If you are still unsure, then make a copy of your design first, as is, and then proceed with only one of them to see what happens. Good luck.

Those stitches were tie offs. Thank you Cuties. I didn't know which stitches the program was referring to until I changed one colour to be the same as the following one and I expected the two of them to become one single color. The program changed the colour but didn't join them e when I was saving the file, a little screen was saying that they were now 44 zero-length stitches instead of 43. At this point I understood what the problem was: I had mirrored one design and sorted all the colours in the layout by hand so that I had two of the same colour left and right , then the following two colours right and left, then two colours left and right, etc. In this way I have created a lot of stitch offs, without realising it. The program didn't join them automatically. I have searched my software (Embird) and found a function that said (more or less) "delete the low length stitches" and this (I think) was the function I needed and then it activated the joining same-colour stitches. Oh my, at this point I felt tired (it was late last night) but happy ....:: -)) Hugs, Lidia