That’s not what lower liquidity looks like. The bonds sell just fine, you just have to lower the price to sell it, such that the effective yield matches the market rate.
Lower liquidity would show up as wider bid/ask spreads, which doesn’t happen in that case.
Maybe you meant this and just wrote it differently, but I'd argue it isn't that it is worth less so much as its liquidity has declined. You felt good enough about that 5% at the time you bought out the mortgage, but now it isn't as good a return as you would get if rates were at 10%, thus it may be difficult for you to sell that mortgage off to someone else given their opportunity cost.
On the other hand, rates (at least in the US) are unlikely to jump even a full 1%,let alone 5%, in such a timeline that you couldn't retrench if you believed you were better off to liquidate and move on to higher yielding assets.