Update: I have found that the problem is with the upgraded resource gatherer. Once the project is stuck at 1 work left, I can complete the project by splitting the caravan and having the group without the resource aggregator complete the project, then re-merge them to move on to the next one.

Thanks a lot for reporting the bug, and to everyone else who did.it is now FIXED and should not happen again, however I had to it the "right way" rather than the quick way.
Basically, I was a bit lazy when I coded this bit and work was an integer, so always rounded to the nearest unit. With ISR2G, Work has become slower so I ended up with fractions that were approximated to 0.
Instead of making plenty of exceptions, I bit the bullet and changed Work to a float. You will now see 2 deciamls when you work on a Site. This means that 0.61 will not be rounded to 1 any more, so it will make things a bit slow if you have very few panws or very low construction level.
Apart from that, it should work well.
I used that opportunity to put more information on each road "leg", so you can plan a bit ahead.
Thanks everyone for your patience !