This can be reproduced with a script like:

insert into #temp select 1 as x, cast(repeat('1', 4000) as clob) y;
insert into #temp select 2, concat((select y from #temp where x = 1), (select y from #temp where x = 1));
insert into #temp select 3, concat((select y from #temp where x = 2), (select y from #temp where x = 2));
insert into #temp select 4, concat((select y from #temp where x = 3), (select y from #temp where x = 3));
insert into #temp select 5, concat((select y from #temp where x = 4), (select y from #temp where x = 4));
– will fail
insert into #temp select 6, concat((select y from #temp where x = 5), (select y from #temp where x = 5))

The #5 clob is unreadable as the backing filestore is removed after insert.