About /ip settings set the rp-filter to loose.
They do not influence NAT, but do not use strict if you use routing tables or complex routing.
I have never had so many NAT rules on one device,
and if I think that if I sum the NAT rules of all my network devices (excluding NAT on CPE),
I do not reach more than 100 rules.
all your rule are like this?
add action=src-nat chain=srcnat comment=srv1 log-prefix=srv1 out-interface=ether7 src-address=10.122.10.121 to-addresses=200.200.9.1
add action=src-nat chain=srcnat comment=srv1 log-prefix=srv1 out-interface=ether7 src-address=10.122.10.122 to-addresses=200.200.9.2
add action=src-nat chain=srcnat comment=srv1 log-prefix=srv1 out-interface=ether7 src-address=10.122.10.123 to-addresses=200.200.9.3
add action=src-nat chain=srcnat comment=srv1 log-prefix=srv1 out-interface=ether7 src-address=10.122.10.124 to-addresses=200.200.9.4
is not better do some netmap with only two rule?, for example:
add action=netmap chain=srcnat src-address=10.122.10.0/24 to-addresses=200.200.9.0/24 out-interface=ether7
add action=netmap chain=dstnat dst-address=200.200.9.0/24 to-addresses=10.122.10.0/24 in-interface=ether7
or using interval / multiple intarvals
add action=netmap chain=srcnat src-address=10.122.10.10-10.122.10.19 to-addresses=200.200.9.10-200.200.9.19 out-interface=ether7
add action=netmap chain=dstnat dst-address=200.200.9.10-200.200.9.19 to-addresses=10.122.10.10-10.122.10.19 in-interface=ether7
add action=netmap chain=srcnat src-address=10.122.10.44-10.122.10.244 to-addresses=200.200.9.44-200.200.9.244 out-interface=ether7
add action=netmap chain=dstnat dst-address=200.200.9.44-200.200.9.244 to-addresses=10.122.10.44-10.122.10.244 in-interface=ether7