WowAce

What version of Grid2 and game type (classic or retail) are you using ?

 Classic TBC

What game client version (windows or mac) and language are you using ?

 Windows, English

What steps will reproduce the problem?

  Enabling 
Did you try having Grid2 as the only enabled addon and everything else disabled?

  Yes

Was it working in a previous version? If yes, which was the last good one?

  No

Do you have an error log of what happened? If you don't see any errors, make sure that error reporting is enabled (`/console scriptErrors 1`) or install [BugSack](https://mods.curse.com/addons/wow/BugSack).

  No

Please provide any additional information below.

 The incoming heal bar is not displayed if my heal is initiated when the target was at full health. Ex. Tank is at full health -> I queue a heal -> tank takes damage and dips to half health -> queued heal goes off. When the tank is at half health, the incoming queued heal is not reflected on the bar. Additionally, sometimes incoming heals extend past the targets raid frame into adjacent raid frames. 

Working fine here, tested with multibars and single bars indicators in latest version 2.0.15 and with a druid class (i dont know the class and grid2 version your are using),  maybe your profile setup is configured in a different way.

Enable lua errors and report the errors here, maybe something is crashing.

No Lua errors to report. Here's a picture as an example. It's entirely possible that I have some configuration incorrect, but the incoming heals indicator seems to sometimes be wildy innacurate or not show up at all, particularly when the target was at full health. In the attached, my incoming heals are colored green. You can see that the druid has +616 overhealing, but the green incoming heals bar is not showing up. 

https://imgur.com/a/ZICfBaW

(excuse the external link)

 In addition, sometimes when a heal that exceeds the targets health defecit is initiated, the incoming heals bar extends past the width of their panel:

https://imgur.com/a/warK07J

I cannot reproduce this issue.

1. Enable lua errors typing into chat:

/console scriptErrors 1

2. You can try out with a new profile (to check if the issue is only happening in your current profile).

3. Disable all other addons.

4. You can send me your profile too (Goto General/Profiles/Export&Import to export the profile to text format).