Regarding leaks, yes, there were rumors of battery pack replacements due to corrections on welds and a separate production issue with ground terminal bolts.[1]
These issues could be due to the different composition of the 3 compared to the S and X - more steel, less aluminum - or with them trying to build a denser automated production line, or just general gremlins setting up new production.
[1] https://electrek.co/2017/09/29/tesla-model-3-production-ramp...