Went to go and keg a German-ish lager and it was infected. My ferm chamber/ cheap chest freezer in my shed died but it has been cool enough that I just wrapped a heater around it to keep it at 54° and did not need it for cooling. I did leave the lid if my freezer open so it would not get too warm
and it looked like flies got under my not so sealed lid and caused the infection. I have always just laid my bucket lids on top and never worried about an air tight seal but I guess having the lid if the freezer down would have saved me.