I have had this problem many times, if I connect the 218 directly to the router the problem went away in my case. But I think you have received the right advice already, the new firmware seems much better in network performance.

Main: DSP8000SE< 218 < Farad Super3 TMCB < PS Audio P10. Room correction: Focus Fidelity.
Second: Fostex Fe206NV2 < Audio innovations 500 valve amp < Wiim Pro +
Study: DSP33 < Reviver < MS200
Server: ROCK + Tidal on NUC, fiber on 2x cisco 2960, HD-Plex LPS.
Gone: DSP7200SEu, DSW, DSP5500mkI & DSP5000mkI, 508.20, 210