It happened to me twice. The first time was in a start-up at the beginning of the century, we were developing an electronic health record and we had outsourced the database abstraction layer to a company in Greece. In the beginning things went fine but after a while the development of the DAL went slower and slower and it became unstable as well.
Eventually the word came out: the main developer of the DAL framework had left the company and, according to the Greek CEO, she had been 'too smart' which meant that nobody understood her code. They had tried adding features but that had made things only worse and the DAL had started to crash randomly.
We tried to take over the framework by ourselves but it was written in Eiffel and the code was a horrible entangled mess. Eventually we rewrote it in Java but, being a start-up, we lost too much precious time already and eventually went almost bankrupt and were bought up by a competitor.
The second time was in a small company whose product was a search engine for consumers. The web layer was written in a mixture of JSF, JQuery and Ajax. While that combination already slowed down development on the front end, the main problem was the performance of JSF on the server. Because JSF is rendered on the backend, it placed a massive load on our server for certain heavily used pages and we just couldn't scale any further. Skipping JSF for a framework that was rendered on the front-end would be the solution but that was a massive refactor for which the company just didn't have enough resources. Eventually the company had to skip their search product and change their business model to a more community based website.