Commented by: @hvlad

Steps to reproduce is very similar to CORE5935, but a bit differs.

Run Firebird 2.5 in Classic or SuperClassic mode and open two terminals.

1) in terminal 1
isql
create database 'core-5936.fdb' page_size 8192;
create table a (id int);
create index idx_a on a computed by (id);

set term ^;

create procedure p_gen_tx(n int)
as
declare i int = 0;
begin
while (i < n) do
in autonomous transaction do
i = i + 1;
end
^

set term ;^
exit;

gfix -write async core-5936.fdb

2) in terminal 1:
isql core-5936.fdb -n
commit;
select current_transaction, rdb$get_context('SYSTEM', 'ISOLATION_LEVEL') from rdb$database;

3) in terminal 2:
isql core-5936.fdb -n
execute procedure p_gen_tx (33000);
commit;

insert into a values (current_transaction);
commit;
set statistics index idx_a;
commit;

select * from a where id > 0;
commit;

execute procedure p_gen_tx (33000);
commit;

4) in terminal 1:
commit;
select * from a where id > 0;

here we get
Statement failed, SQLSTATE = 08006
Error reading data from the connection.

Commented by: @hvlad

Fix is frontported into v3