Unbound unresponsive when AXFR RPZ

[Arnaud Gavara]

Hello,
I am using Unbound in version 1.13.1 with RPZs (configuration below).
I observe that for a relatively large RPZ (around 300k entries), Unbound no longer responds to client requests during the zone is AXFR transferred. It lasts on average 1 second, but it's enough to lose a lot of requests.
Would it be possible to optimize this downtime?
I have already looked and applied the optimization guide (https://nlnetlabs.nl/documentation/unbound/howto-optimise/) but there is nothing relating to the AXFR transfers of the zones.
I specify that the master server performing the transfer of the zone is local and I do not think it's the source of the problem. 

Bonus question, are there any plans to be able to do IXFR? This could be useful for RPZs with a certain size.

Regards,
Arnaud

Configuration type:
rpz:
        # RPZ MALWARE
        name: rpz.malware
        zonefile: /var/lib/unbound/zones/rpz.malware
        master: a.b.c.d
        allow-notify: a.b.c.d
        rpz-log: yes
        rpz-log-name: rpz.malware
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