That sucks. Think you try and get the lender to reimburse you the $600 as an act of good faith and with the hope of doing future business with you. If you’ve met the lender on the forums, I’m sure they will be concerned with maintaining their reputation for doing what they say (doesn’t seem to be the case in this scenario) or at the very least taking care of their clients when they’ve made a mistake that is costing you $.
If not, I think you take the hit. It isn’t that much in the grand scheme of things and you may have saved yourself from overreaching. Think you said yourself that this deal was “okay” at the lower cost of capital (and even less appealing at 8%). If you’re reaching for yield and paying too much, this could be a blessing in disguise (albeit one that cost you a couple hundred) and you may be glad that this deal ended going away from you. This last statement is mostly driven by my general view that we are late in the cycle and the market seems to be cooling.