No, because NRZI is not the same as NRZ.
Each '1' in NRZI is a toggle regardless of rate. So "1111" cannot be confused with "11111111" because you cannot confuse 4 toggles with 8 toggles.
But that's not the whole story : in your example (receiver at double rate) "1111" (sent 4 toggles) would be received as "10101010" (4 toggles, 4 spaces between toggles). (OK you edited the question to reflect this)
But this isn't a synchronisation error per se : synchronisation doesn't guarantee the ability to decode arbitrary signals : some a-priori knowledge of the approximate data rate can be assumed (or specified in the coding scheme) and 2:1 variation prohibited.
Then "1111" is self synchronising (the first toggle tells you when the first bit appears) and subsequent toggles keep you aligned to track clock errors, but "0000" is patently not because nothing happens.
"00001111" is still not self synchronising; so there must be something else like a preamble or idle pattern to provide framing (i.e. identify the start of a message or packet)