lnd: [bug]: unable to forward, wrong "insufficient bandwidth"

Background

I have more than enough liquidity in one of my channels and should be able to serve outgoing forward requests. However, this doesn’t work. Instead, lnd reports “insufficient bandwidth”. Details below.

Your environment

• lnd v0.15.4-beta
• Linux server 5.10.0-13-amd64 #1 SMP Debian 5.10.106-1 (2022-03-17) x86_64 GNU/Linux
• bitcoind v23

Steps to reproduce

Get forwarding request out via channel X.

Expected behaviour

Forwarding request is served, fees are earned, local balance is reduced.

Actual behaviour

“insufficient bandwidth to route htlc: x is larger than y” (canSendHtlc in link.go)

First observed failure:

• Date: 2022-10-25 18:31:17
• Requested amount: 188,242,405 msat
• Available (according to lnd): 3,005,999 msat

Balance at 2022-10-25 18:29:25+02:

• local: 9,897,025 sat
• local reserve: 100,000 sat
• remote: 100,078 sat
• remote reserve: 100,000 sat

Most recent failure:

• Date: 2022-11-03 13:18:31
• Requested amount: 50,024,602 msat
• Available (according to lnd): 2,843,999 msat

Balance at 2022-11-03 13:14:47+01:

• local: 9,896,568 sat
• local reserve: 100,000 sat
• remote: 100,712 sat
• remote reserve: 100,000 sat

lncli listchannels:

{
            "active": true,
            "remote_pubkey": "03627ebe50fc6eb80b0caab0c3714958c701eda735e3c29588e83150d6d4a93976",
            "channel_point": "db8a9a4d483e0fd0c84e5a004d51dd51ecbb113329729c18db6a5112bab61a4f:0",
            "chan_id": "834535922707529728",
            "capacity": "10000000",
            "local_balance": "9891564",
            "remote_balance": "108241",
            "commit_fee": "195",
            "commit_weight": "724",
            "fee_per_kw": "269",
            "unsettled_balance": "0",
            "total_satoshis_sent": "2036708",
            "total_satoshis_received": "11928272",
            "num_updates": "9950",
            "pending_htlcs": [
            ],
            "csv_delay": 144,
            "private": false,
            "initiator": false,
            "chan_status_flags": "ChanStatusDefault",
            "local_chan_reserve_sat": "100000",
            "remote_chan_reserve_sat": "100000",
            "static_remote_key": true,
            "commitment_type": "STATIC_REMOTE_KEY",
            "lifetime": "174093",
            "uptime": "174093",
            "close_address": "",
            "push_amount_sat": "0",
            "thaw_height": 0,
            "local_constraints": {
                "csv_delay": 144,
                "chan_reserve_sat": "100000",
                "dust_limit_sat": "354",
                "max_pending_amt_msat": "18446744073709551615",
                "min_htlc_msat": "0",
                "max_accepted_htlcs": 30
            },
            "remote_constraints": {
                "csv_delay": 1201,
                "chan_reserve_sat": "100000",
                "dust_limit_sat": "546",
                "max_pending_amt_msat": "9900000000",
                "min_htlc_msat": "1",
                "max_accepted_htlcs": 483
            },
            "alias_scids": [
            ],
            "zero_conf": false,
            "zero_conf_confirmed_scid": "0"
        }

lncli getchaninfo:

{
    "channel_id": "834535922707529728",
    "chan_point": "db8a9a4d483e0fd0c84e5a004d51dd51ecbb113329729c18db6a5112bab61a4f:0",
    "last_update": 1667403066,
    "node1_pub": "027ce055380348d7812d2ae7745701c9f93e70c1adeb2657f053f91df4f2843c71",
    "node2_pub": "03627ebe50fc6eb80b0caab0c3714958c701eda735e3c29588e83150d6d4a93976",
    "capacity": "10000000",
    "node1_policy": {
        "time_lock_delta": 99,
        "min_htlc": "1",
        "fee_base_msat": "0",
        "fee_rate_milli_msat": "1",
        "disabled": false,
        "max_htlc_msat": "10000000000",
        "last_update": 1667403066
    },
    "node2_policy": {
        "time_lock_delta": 34,
        "min_htlc": "1",
        "fee_base_msat": "0",
        "fee_rate_milli_msat": "135",
        "disabled": false,
        "max_htlc_msat": "104096134",
        "last_update": 1667143395
    }
}