Subselect or union operations impossible to execute in HADR standby - db2

Question

Trying to execute some queries in a HADR database with RoS (Read only Standby) with a union operator or with a subselect, I got the error SQL1773N reason code 5.
What is the reason? they are operations that do not generate writes.
Union
with hist(start_time, operationtype) as (
select start_time, operationtype
from sysibmadm.db_history
where operation = 'B' )
select 'delta', timestampdiff(8, current timestamp - char(timestamp(max(start_time))))
from hist
where operationtype = 'D' or operationtype = 'E'
union all
select 'delta', timestampdiff(8, current timestamp - char(timestamp(max(start_time))))
from hist
where operationtype = 'I' or operationtype = 'O'
Subselect
with hist(start_time, operationtype) as (
select start_time, operationtype
from sysibmadm.db_history
where operation = 'B' )
select 'delta', operationtype, start_time, timestampdiff(8, current timestamp - char(timestamp(start_time)))
from hist
where start_time = (
select max(start_time)
from hist
where operationtype = 'D' or operationtype = 'E')

Answer 1

This seems to be a problem specific to sysibmadm.db_history.
Tried the following union all and subSelect on Standby with ROS enabled, and both worked fine
CREATE TABLE TAB101 (
id bigint NOT NULL,
createTimestamp TIMESTAMP NOT NULL,
primary key (id))
insert into tab101 (id, CREATETIMESTAMP) values
(1, current timestamp - 35 minutes),
(2, current timestamp - 30 minutes),
(3, current timestamp - 25 minutes),
(4, current timestamp - 20 minutes),
(5, current timestamp - 15 minutes),
(6, current timestamp - 10 minutes),
(7, current timestamp - 5 minutes),
(8, current timestamp)
with tempTab101 (id, CREATETIMESTAMP) as (
select id, CREATETIMESTAMP from tab101
)
select id, CREATETIMESTAMP from tempTab101
where id > 1
union all
select id, CREATETIMESTAMP from tempTab101
where id <= 10
with tempTab101 (id, CREATETIMESTAMP) as (
select id, CREATETIMESTAMP from tab101
)
select * from tempTab101
where id = (
select id from tempTab101 where id=2
)