To one sig fig that's 55 feet difference in location. GPS uses WGS84 and GLONASS uses PZ90. "Officially" the difference is supposed to be less than 45 feet all the time and generally less than 15 feet. So, I don't think that's the problem.
There seem to be issues with stepping time, and long term alignment seems to be deprioritized over short term quality. Better to have better data today than to have better long term drift over a decade. So all the systems kind of "free run" very close to each other but measurably different. It does not seem that very long term drift adjustment was baked into the cake of any nav protocol, probably because its not navigationally useful.
That time is hard, I think. So the network itself has needs, you can't just shift all clocks by 55 ns. So instead, an offset is broadcast that tells you what you need to subtract/add to get to UTC.
