We're looking into this. We haven't changed anything telegram-related on our end, and our load hasn't really changed either, but telegram's servers recently started issuing some errors claiming that our bots are submitting too many requests. Some telegram messages are getting dropped on the floor as a result. (We try 3 times and give up after that.)
We're nowhere near their documented load limits. (We're at about 3-5% of the documented values.) I've reached out to their bot support to ask what's going on, but from what I've read we're not very likely to get a reply :-(.
In the the meantime, we've added a number of new telegram bots. Without knowing why the existing bots are considered overloaded (i.e. is it really our traffic, is it a temporary problem on their side, or have they changed what limits apply per bot and not documented it yet) we're not sure if this will help.
Can a few of you try moving to a new bots and see if that solves the problems for you?
Moving from one of the old bots to a newer one requires cancelling and signing up with a bot again. If you want to try this, send a message saying "/cancel" in the existing chat. You should get a confirmation that you'll no longer receive alerts. Then, click your profile pic in the top bar and choose "receive alerts in telegram" as you did before ... telegram should open and then you need to click the "start" button, and you should get a confirmation that you're signed up. (Signing up again is easiest done on a phone, where you already have the telegram app installed. Clicking the link will open the telegram app, and you should see the "start" button at the bottom of the screen.)
Note: If this suggestion turns out not to help, I might delete this message from the forum after a few people try it.