The issue comes up when starting apache with the mod_lbmethod_byrequests enabled while mod_proxy module is NOT enabled. The error: Cannot load lib64/httpd/modules/mod_lbmethod_byrequests.so into server: /usr/lib64/httpd/modules/mod_lbmethod_byrequests.so: undefined symbol: ap_proxy_balancer_get_best_worker. There was a post describing a workaround by loading mod_proxy before the mod_lbmethod_byrequests module, the problem with this approach is that now you will have mod_proxy (and a matching bogus config pointing /whatever to a non existent backend server) just to get mod_lbmethod_byrequests working. The bottom line is that mod_proxy should NOT be a prereq for using mod_lbmethod_byrequests as it May NOT be needed. Please feel free to correct me if I am totally missing something
Change your module load order to load mod_proxy first. It is not possible to use lbmethod modules without mod_proxy. In 2.4.35 the load order dependency is corrected; but mod_proxy is still necessary. What purpose do you have in loading lbmethod's if you are not loading mod_proxy_balancer, and ergo mod_proxy, into the given server instance?