Double check your coach settings
I usually do many XP/day, but I have my coach set to 1XP because some days I'm tired or ill. It's been set to 1 for months if not years.
I logged in today to discover that somehow it's set on 20 8-o Granted, like I say, it would not usually be a problem and I regularly check I have a streak freeze enabled, but I could easily have lost my streak by just doing one lesson a day and not realising it had changed.
I don't know if this is a bug, I'm going to report it to Duolingo, but I'm sure I'm not the only creature of habit who has had my coach set on one thing for so long that I could easily have been caught out. As such, I think it would be a good idea for folks to check their coach settings just in case!
Simply using the app has never reset my goal before, and it's been set to 1XP for, like I said, months if not years. If I was to go into the streak settings in the app, then yes, that can muck it up, but I haven't done that in a year or more.
Simply using the app (I do a mixture of app and website almost every day, and have been doing so for several years now) has never reset it before.
Mine has been on 1XP for ages without an issue - swap regularly between the app and the website, and it's never changed before. I wouldn't worry about it, just... keep an eye on it!
I've swapped between the app and website several times today to check, and so far it's holding on to my 1XP target, but I'm going to check it on the regular just in case.