Do you mean once you add the working testcase(RFT script) to a test suite(no other test cases), then it will hang at 70%? And if you run the same test case after hanging, it will work again?
One difference between running TestCase and test suite with that testcase is that the path used by the adapter to run the script could be longer when running test suite. That could be crucial in a Windows' environment given that there is limitation on Windows.

What is your RQM version, RFT version and RFT testing objects(HTML or jave) and if the script is recorded one or it is manually created?

. One potential cause is that it hits the Windows' path limitation and you may want to check if you can shorten the name of testscript, test case and test suite
. another potential cause is the lower version of RFT(such as v8.5 or lower) and there is defect to cause the failure in test suite.
.  There is also report that adapter could be corrupted(version around 8.2 RFT) and by removing the below(backup before removing) file may help:
- go to:
 C:\document and settings\all users\Application Data\IBM\RQMConnectivity
and remove the file rqmadapter.
C:\document and settings\username\Application Data\IBM\RFT and remove
the file RQMadapterOptions.pref and rational_ft.pref files.

. if it works with one specific test case but test suite has more test cases included and it starts to hang, potentially something can be related to multiple test scripts in which manual scripts may not release the created objects properly and it results in the heaps not reset and kept increasing in the continuous executions(multiple scripts). In that case, a close check on the scripts is required.

. In some cases, if RQM project area has some special character such as & etc in its name, the result can not be passed back to the right project and it will appear to hang during the logging stage. You will need to make sure RQM project has the name without special characters.

In many cases, the problem is more likely to be on RFT adapter and tracing on RFT side may be helpful to identify what's wrong. In that sense, you may want to work with Rational support to find out what's wrong.