TP-Link Deco BE63 — Wired Backhaul Issue with 1G Media Converters

Setup:
- 2x TP-Link Deco BE63 (purchased June 1 2026)
- TP-Link TL-SG108S-M2 8-Port 2.5G unmanaged switch
- 2x Bidi 1G media converter pairs (1.25G/s Bidi Gigabit Single-Mode)
- Single mode simplex Bidi LC SFP modules (blue/yellow matched pairs)
- Invisible single mode simplex fiber cable runs
- SC to LC adapters at media converter ends
- Patch panel

The Problem:
Kaia's Room BE63 satellite unit refuses to establish wired ethernet backhaul through 1G media converters. Link light on media converter never comes on. Unit always falls back to wireless backhaul showing 5GHz/6GHz connection to Living Room main unit.

Everything We Tested/Replaced:

Hardware replaced:
- 2x media converter pairs — both brand new, same result
- Multiple ethernet cables
- Brand new fiber cable run
- SC adapters swapped between working and non-working run

Tests performed:
- Tried all 4 ethernet ports on Kaia's Room BE63
- Tried multiple switch ports including native 1G ports
- Bypassed patch panel completely with direct ethernet from switch to media converter
- Disabled loop detection on switch (physical switch on back of TL-SG108S-M2)
- Cleaned all fiber connectors and SC adapters
- Swapped SC adapters between living room and Kaia's room runs
- Swapped fiber cables between living room and Kaia's room runs
- Swapped SFP modules
- Verified blue/yellow Bidi SFP pairing correct on both ends
- Factory reset Kaia's Room BE63
- Rebooted switch, both Decos, both media converters

Critical Finding:
When connecting Kaia's Room BE63 directly to Living Room BE63 via straight ethernet cable — wired backhaul establishes immediately. This confirms:
- Kaia's Room BE63 ethernet ports are functional
- Switch, cables, and infrastructure are functional
- Problem is specifically BE63 compatibility with 1G media converters

Conclusion:
BE63 ports are 2.5G and appear unable to auto-negotiate down to 1G when connecting through 1G media converters. Deco to Deco works because both are 2.5G. Media converters max out at 1G and the BE63 will not step down to match.

Living Room BE63 works through identical media converter setup — this is the only unexplained variable.

Support Case: Already open with TP-Link support. Switch team following up.

Question for Community:
Has anyone successfully used 1G media converters with the BE63 for wired backhaul? Is there a firmware fix or workaround? Do we need 2.5G media converters specifically?