Hashtags only work if you select it from the popup. That inserts the tag. It does not do auto inserting of tags. Will review adding support for auto hashtaging in a future release, but it's tricky as it forces assuming intent. Typing quickly shouldn't matter it should still popup once the HTTP call to your server completes.
forge.joomlapolis.com/issues/9399
This was designed after Facebook and similar social media platforms not Twitter which is why it requires an explicit action to insert a hashtag. However will try to implement assuming intent as per the above feature ticket in a future release. Likely will do so with a parameter to toggle on/off since some many not want this.
Additionally CB Activity 5.0 hashtaging is still supported. You can enable it within CB Activity > Streams > Legacy by toggling on "Hashtag Parsing". This is a slower process than the new implementation because it has to process every single post on display looking for what it thinks is a hashtag so it might have misses, but it will restore the old behavior.