Since you asked this question, there must be something specific in your posts which are causing the problem. Several things can happen:
1. If you take too long, you can lose the connection (type outside Yahoo and cut/paste to get around this)
2. You have a bad cache file on your system, clean and reboot.
3. Just copy your question, refresh the page and paste it in again.
4. Certain links will cause problems, post without them and add as updates.
5. Symbols such as % will cause problems on mobiles. Spell it out.
6. On mobiles, try Desktop mode.
Sometimes when that happens, the question did submit, the problem is the next screen does not come up properly.