[CRASH] umap's get unloadable very easily

I have big problems to work on streaming map pieces without loosing hours of work randomly. Suddently just umap may just stop loading without crashing the whole editor. Just doing normal work - tweaking landscape and removing/adding meshes.

Been sending crash reports with
LoginId:f87b756443f95ce9986941a672fe5264

[2017.05.13-21.40.40:529][ 5]LogWindows:Error: Unhandled Exception: EXCEPTION_ACCESS_VIOLATION reading address 0x00000018
[2017.05.13-21.40.27:440][ 5]LogInstancedFoliage:Warning: Instance base cache - integrity verification(3): Counter: 928 Size: 253, InvSize: 98 (Key: 00000000-00000000-00000000-00000000)
[2017.05.13-21.40.27:440][ 5]LogInstancedFoliage:Warning: Instance base cache - integrity verification(3): Counter: 928 Size: 253, InvSize: 98 (Key: 00000000-00000000-00000000-00000000)
[2017.05.13-21.40.27:440][ 5]LogInstancedFoliage:Warning: Instance base cache - integrity verification(3): Counter: 928 Size: 253, InvSize: 136 (Key: 00000000-00000000-00000000-00000000)
[2017.05.13-21.40.27:440][ 5]LogInstancedFoliage:Warning: Instance base cache - integrity verification(3): Counter: 928 Size: 253, InvSize: 136 (Key: 00000000-00000000-00000000-00000000)
[2017.05.13-21.40.27:440][ 5]LogInstancedFoliage:Warning: Instance base cache - integrity verification(3): Counter: 928 Size: 253, InvSize: 194 (Key: 00000000-00000000-00000000-00000000)
[2017.05.13-21.40.27:440][ 5]LogInstancedFoliage:Warning: Instance base cache - integrity verification(3): Counter: 928 Size: 253, InvSize: 199 (Key: 00000000-00000000-00000000-00000000)
[2017.05.13-21.40.27:440][ 5]LogInstancedFoliage:Warning: Instance base cache - integrity verification(3): Counter: 928 Size: 253, InvSize: 199 (Key: 00000000-00000000-00000000-00000000)
[2017.05.13-21.40.27:440][ 5]LogInstancedFoliage:Warning: Instance base cache - integrity verification(3): Counter: 928 Size: 253, InvSize: 201 (Key: 00000000-00000000-00000000-00000000)

Sometimes it says something about splines - most likely landscape tool splines since those have been unstable in previous builds too. But umaps might get broken too without doing any changes to splines.

I dont know how to make repro, this happens very random way with dense detailed streaming maps.

Seems like something going wrong with instanced link textfoliage?

EDIT: To add more info. I used the new tool in foliage to place instances (speedtree trees) one by one.