OP could have changed exercise habits, leading to more frequently outdated GPS almanac data.
Otherwise, newer OS versions could have degraded the fix algorithm for older Watch-models.
If newer hardware comes with cellular connectivity, newer OS version could assume that by default and not prioritise (or test) backward compatibility with older Watch-models.
Otherwise, newer OS versions could have degraded the fix algorithm for older Watch-models.
If newer hardware comes with cellular connectivity, newer OS version could assume that by default and not prioritise (or test) backward compatibility with older Watch-models.