[tvb]

Don't worry. This happened once before in 2003 [1].

UTC has provisions for positive or negative leap seconds; that works fine. GPS runs without the hassle of leap seconds; that works fine too. GPS users often want to know UTC, so GPS also broadcasts the difference between GPS time and UTC; this works fine.

All of this is in the GPS spec; almost all GPS receiver firmware gets it right. But there is a weird edge case that is hard to test. Specifically if there has been no leap second for 256 weeks (1792 days, ~5 years) inadequately tested GPS receiver firmware could mess up. It happened to one make/model GPS receiver in 2003. [1] It could happen again later this year, in 2021.

The math is fun. The most recent leap second was 2016-12-31 (MJD 57753). 8 bits or 256 weeks later(1792 days, not to be confused with Ramanujan's taxi number 1729) will be 2021-11-27 (MJD 59545). So shortly before, or on, or after that date it is possible a faulty GPS receiver will misrepresent a leap second or miscalculate UTC. GPS positioning and navigation is likely completely unaffected (because it avoids leap seconds entirely).

[1] http://leapsecond.com/notes/leapsec256.htm