I have a Synology DiskStation with Media Server connected by wire to ASUS RT-AC87U router which also has two Wi-Fi bands, 2.4 and 5 GHz used by Apple devices. All connected devices are in the same IP network 192.168.0.*.
Infuse 4 and 5 on iPhone, iPad and AppleTV connected to the 5GHz band cannot detect neither DLNA nor SMB server, but it perfectly detects them when connected to the 2.4GHz band. After adding NAS folders to favorites on 2.4GHz and switching back to 5GHz they still can be accessed by Infuse, so this temporary band switching can be used as a workaround, but the behavior is still strange. I checked some other players (nPlayer for example), they have no problems in detecting DLNA/SMB on both bands, so it is not a router or device issue.