I strongly recommend reading the article (in two parts):
"ARMAMENT NOTES No.2 The Lewis Gun in British service", in Cross and Cockade international vol 19-2 and 19-3. These are cheap to buy in pdf form from
https://www.crossandcockade.com/store/ at a very cheap price (and they are available in a few minutes).
You can also check this one:
"There I was, dead on his tail when..." in Over The Front vol 8-1., as this one looks at the causes and possible remedies as printed in official publications (in 1917-1918). Of course, if you don't have this issue, you'll need to order from the USA and it takes long to travel...