Pixel 2 XL/Textra Group messages create new texts to new phone numbers

Hey so this also happened on my Nexus 6, but has also been happening on my Pixel 2 XL. Using Textra app. Occasionally when sending group messages, my phone will seemingly create a new group. This new group will consist of some of the original members, will drop existing members, and instead will create new recipients.

Here's where it gets a little odd. The new recipients have the same phone number as the original, but it will change their area code to match mine. so someone with the number 751.xxx.xxxx will be dropped and replaced with someone whose phone number is 617.xxx.xxxx. It has lead to some interesting responses.

Was wondering if anyone else has experienced this issue, and if anyone knows a fix. Apologies if this has already been answered in a previous post, looked back a bit and didn't see anything.

I never heard of it, and I've been around Android for a while. Try emailing Textra at help@textra.me and asking them. Give them the first 2 paragraphs in your post, so they can run it on a N6 or a P2 (or 2XL) and see if it somehow has a bug doing that.
(Use the real area codes - it could be as simple as 751 causing a problem, or a number without a 1 in front causing a problem [or a number with a 1 in front causing a problem, if you have 1s on all your numbers (you shouldn't have - a cellphone call on a US or Canadian carrier assumes the 1)]. If you're not a software developer, you'd be surprised at the bugs a simple typo in the code can cause. [Like 6 months of finally finding out that an upper-case A at the start of the color in the color field of a particular database table blowing the program up. 15 seconds of fixing it, but 6 months of finding the cause. And they wonder why developers have coronaries. No, it's not from sitting at a desk all day.])