Looks like Citrus infectious variegation virus
I have had it appear in unbudded rootstock seedlings here, usually a side branch or a terminal leaf goes V.
( sorry I have been binge watching Z nation, the zombie series ).
Always hoped it was real variegation, but was not.
Sometimes appears in very young seedlings, same as above, after a while it is obviously not true variegation.
It does seem to appear spontaneously in these soon after germination, so might be another cause ?
As others here have said, it could be stress induced, or the massive new flush has released it into many growing points.
Is there any lower clean area of the plant you can prune back to ? (Sterilise cutters so you don't reinfect.)
Any signs that it is fading out in newer growth, and the plant is recovering ?
Do you have many other Citrus ? if not it is probably not much risk to other Citrus plants.
Not sure if it is a latent virus, or spread by vectors.