Further Detail:  Apparently, this only happens if the text was created using the WEBSITE version of Strava.  For two recent activities, I wrote the text using my laptop and triggered the bug: the “see more” link was not available on the app, making the rest of the text impossible to see on the app.

Workaround: I coped the text to a separate file, then deleted all text from the activity.  Copying back the same text, using the Android phone app, resulted in the “see more” link appearing.  So, something about creating the text on the website may have triggered the bug (at least that’s my hypothesis).

I’m also seeing this issue regularly but I have also had it happen when editing activities from the mobile app directly. And the workaround mentioned by ​@Cyclo_Saurus doesn’t seem to fix it for me...

Good call in mentioning that.  I have also had this issue using the mobile app once or twice - much less frequently. I had not seen that behavior when I posted here for the first time.

For me, I've noticed it's more likely to happen when... I have quite a bit of text in the description, I use @ to mention people, and/or have spaces between paragraphs. I have no idea if that's related though. I'm more likely to do all of those things in a web browser than when using the mobile app.  The only workaround I found was experimenting: removing the text, trying again without any blank lines between paragraphs (all one solid block of text) and without any mentions of people (@___), etc.  Maybe it's just by chance, but eventually I've been able to get it to post properly.  It's still really annoying!

This is also happening to me 6/15. I did not create the text on web which OP had thought was causing the problem. I made the description in the android app, and it cuts off the end without a "more". I had a typical text description followed by tagging people, where it cut off. I have no idea if the people I tagged past that actually got tagged or not.