what fertilizer are you using? have you only had 2 vegetative flushes this year so far?
you might get new growth soon, take some pictures of the new growth and also of the leaves as they are starting to harden
two of my container lychees suffered nearly complete die back from damage early this year. the Mauritius promptly bounced back with growth every 5 weeks - having a warm winter/spring pribably helped. the sweetheart had much less vigorous growth for 3-4 months and even had leaf tips that eventually browned - this was very surprising to me because the Mauritius (and all my other container lychees) didn't brown.
about 1-2 months after the leaves had brown tips and even some yellowing, it has started putting out constant vegetative growths and behaving like its peers.
I've killed a number of container lychees by misinterpreting leaf changes and using the wrong fertilizer. wanted to throw in my two cents that I've seen containers lychees have "unhealthy" looking leaves as its preparing to restart growth after suffering damage. I think it might be the tree consolidating nutrients and redistributing to areas that had died back most (so that the canopy grows back in an even manner)
Yes, it had 2 flushes this year. one early in the year and another about 2.5 months ago. during the first flush I thought it was fungal so I sprayed it with copper - twice, one week apart. 98% of that flush did not make it. most young tips appear torched. the remaining leaves started having these brown spots. at the same time I apply liquid fish fertilizer weekly, same rate as I use on my other container tropical trees. after I trim back on all dead branches I moved the tree to 50% shade due to the extreme hot weather as I thought maybe it got sunburned. I continue to use liquid fish weekly on all of my container trees until the start of summer. all of my other trees are healthy and happy, cherimoya, longan, guava, jabo, and etc. the 2nd flush came and it was like the first. nearly all new growths die and the tree suffer further die back as I trim off more dead branches. the tree has maybe 1% leaves remaining and none look healthy. I figure if I dont do something I will lose it. so I re-pot it with Pro Mix. I have not use any fertilizer or chemical since re-pot. just light water every couple of days.