Getting toast message with text sending

I'm using Asus 551 with lollipop. I have numerous apps installed. Recently, I started getting toast notification with the text **Sending...**. This usually occurs when I'm using Facebook, whatsapp and such apps. It seems fishy. I recently uninstalled es file explorer after a similar issue was reported by users. It was showing similar toast with some Chinese text. Is there a way I could find out what app is causing this? Here is a screen shot: I tried the dumpsys command, as suggested by @Firelord. Then used some of the apps, got the **Sending...** toast a couple of times, then again ran the dumpsys command, but there was no difference in the log. Here is how it looked before and after: