This sounds like a bug which was fixed in the latest connector release 7.0.2. If you are not using 7.0.2, try to install it. This bug was on the SAP side of the connectors, so you have to install both the SAP transports and the Windows part.
The bug which was fixed affected only Message server connection, so this must be something else.
You can check the parameters affecting the shared Export/Import buffer in the SAP system? The Export/Import buffer is used by the SQL connector. If the values are too low it can affect the connector. Otherwise I suggest to contact the Qlik Support!
Check the SAP note 702728 - Profile parameters for export/import buffer instances.
NOTE: when the parameters have been changed, restart the SAP system to activate the new values.
The following parameters are important: rsdb/obj/buffersize Syntax for correct size: PHYS_MEMSIZE * 1024 * 0,01. For example, if the server has 35 Gb of memory, the correct value should be 358400.
rsdb/obj/max_objects Syntax for correct size: rsdb/obj/buffersize / 4. Correct value based on rsdb/obj/buffersize of 358400 = 89600.
rsdb/obj/large_object_size Default: 8192. Because this default value has proven to be too small, it has been changed as follows in kernel patches: - As of kernel Release 7.40 PL 68, 7.41 PL 35, and 7.42 PL 3, the default has been increased to 250000.
The parameter values can be checked in transaction RZ11 or in transaction ST02.