My parts:
- Cable Modem ES2251 DOCSIS 3.1 eMTA (frequency 108 -1002MHz per manual)
- Splitters is GE 5-2500MHz
- MoCA filter 35-45dB of rejection in the MoCA 1125-1525Mhz
Initially, I added the MoCA PoE Filter and the two Splitters, and it all tested good with full speed Internet. As soon as I install one of the WF-803M, the modem will go offline, and it will not sync with ISP. If I install both WF-803M, the Pwr and MoCA LED stays on, while LAN flashes, and I can ping upto the router. If both WF-803M are disconnected, the modem syncs and all work without issue.
Below diagram is my setup. Please help.

Short answer: Install a separate (second) MoCA filter directly on the DOCSIS 3.1 cable modem as a prophylactic, to protect the DOCSIS 3.1 modem from the MoCA signals. (With the DOCSIS 3.1 spec overlapping the MoCA frequency range, MoCA signals are a coaxially transmitted disease to a D3.1 modem.)
p.s. Above presumes use of a DOCSIS 3.1 modem only, absent the provider actually employing DOCSIS 3.1 frequencies above 1002 MHz. (Which should be the case of the OP, since the "PoE" MoCA filter — actually installed at the cable signal point-of-entry — would have been blocking D3.1 signals, anyway.)
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Longer...
DOCSIS vs MoCA:
* MoCA Extended Band D: 1125-1675 MHz
* DOCSIS 3.0: up to 1002 MHz
* DOCSIS 3.1 “initial rollout”: up to 1218 MHz
* DOCSIS 3.1 “full”: up to 1794 MHz
More info here: https://www.reddit.com/r/HomeNetworking/comments/uvzqda/not_sure_if_this_mocapoe_filter_my_isp_let_me/i9pei20/
Will feedback to you by email. Thanks.