Signed up to say I'm having the same problem on my wrt3200acm since updating the firmware to this version.
Pinging gives "destination host unreachable". Other connections timeout after a while opposed to giving a not found error.
I haven't tried other wired clients (only my desktop pc is wired) but I cannot connect to any devices on my LAN. This includes smb shares, VNC, webservices on Raspberry Pi's, SSH or telnet to any device other than router itself is unsuccessful. So basically I've tried a variety of different devices & ports.
What's strange is it does work for a limited time after I've done a router reboot.
Additionally I have OpenVPN client is use with policy based routing. It appears to make no difference if I have VPN client enabled or disabled.
I have a (WIFI) network connected printer, which doesn't work as wifi clients can't find each other in the network, it's like if AP Isolation was turned on. (I already checked from the UI and it shows as Disabled)
Another new guy (well, had an account, but been away from the forum for a while) with the same issue.
Things were working fine with the WRT54GL repeater bridge units here, but the new WRT3200ACM will "see" the repeaters and the printers behind them only for about 10-20 pings, and then they disappear. TCP traffic also cannot connect.
As the OP did, I backed down to the old Feb release and all seems OK.
Still works fine on DD-WRT v3.0-r35898 std (05/07/18 on WRT3200ACM.
All releases following this one have issues - can't ping anything, wireless disconnects for Android phones and so on.
So check out the r35898.
Currently, I run the build r36808. Wireless is stable but I can't ping the android devices on my network from the router of from Linux/Windows wired devices. Other wireless devices (Wireless radio) can be pinged. Unfortunately, that prevents application running on my Windows PC to interact with my android phone.
I tested the build r35898 using the same wireless settings and indeed I can ping the Android devices. Unfortunately the wifi network was unstable. My wireless radio was even unable to connect.
Here are my settings:
5.0 Ghz Mode AP, Network mode AC/N-Mixed, Ch. Width VHT80
2.4 Ghz Mode AP, Network mode Mixed, Ch. Width Full(20Mhz)
Wireless channel are NOT set to auto.