3126608 - Error in phase GENBUFFER_PREPUT: Addtobuffer failed for XXXXXXXXXX

During an Upgrade with Software Update Manager (SUM), the SUM tool stops with the following errors:

SAPupConsole.log:

Severe error(s) occurred in phase PREP_INTEGRATION/GENBUFFER_PREPUT!

Last error code set:
Calling 'D:\usr\sap\***\SUM\abap\exe/tp' failed with return code 247, check GENBUFFE.ECO for details

GENBUFFE.ECO :

EXECUTING D:\usr\sap\***\SUM\abap\exe\tp.EXE "pf=D:\usr\sap\***\SUM\abap\var\SHADOW.TPP" addtobuffer SAPK750EAS "buffer=PREPUT.BUF" u126
This is D:\usr\sap\***\SUM\abap\exe\tp.EXE version 381.22.22 (release 753, unicode enabled)
Addtobuffer failed for SAPK750EAS.
Datafile not existent (cofile exists).

SAPup.log:

CURRENTPHASE PREP_INTEGRATION/GENBUFFER_PREPUT

...started at 20200824151353

# Command addtobuffer for transport 'SAPK750EAS' on buffer 'PREPUT.BUF' stamp ''.

...finished at 20200824151354 with status ABORTED.

# Error message set: 'Calling 'D:\usr\sap\***\SUM\abap\exe/tp' failed with return code 247, check D:\usr\sap\***\SUM\abap\log\GENBUFFE.ECO for details'

Addtobuffer, SUM, PREP_INTEGRATION/GENBUFFER_PREPUT, GENBUFFE, Datafile not existent, cofile exists, return code 247 , KBA , BC-UPG-TLS-TLA , Upgrade tools for ABAP , Problem