That's pretty common for me. Try to purge all caches & then update it. If that doesn't work, then purge all caches & close d tab restart d browser & update ublock origin. Hope that will resolve it.
& btw that sign signifies network error. Network error may mean many thing. If,like me, you've multiple extensions which are there for same reason or any web(traffic) scanner or you are using ublock origin for long time, then it's bound to happen.
I've jst noticed you have I Don't Care About Cookies extension. It may or better to say it is messing the update process. Cookies is needed for ubo update as much as I know. Try to disable it during ubo update. & ubo does need access to its indexedDB database to update itself. If your browser is blocking it then I don't know. Btw can I ask you which browser you are using if it's not a personal question?
Purging cache resolved it. To be honest, that's sad. I smelt something interesting. It seems ubo doesn't purge its cache.You may use dev tools to check it manually.
I thought at that time, there must have to be some sorta limit or cap on memory usage of indexedDB. But if jst purging cache resolved it then no way it's because of limit of memory usage.
Anyway, if it has resolved the issue then great. That is pretty easy fix but... Sorry if I have made you wait a bit. Which I have.