Finally I have found time to test out the lede-mt300n-v2-clean-2.264.bin firmware release.
The WiFi is now very stable with good performance. Well done to the team, a lot of hard work went into this I can see 
One small problem now is the wifi driver dumping loads of debug messages into the kernel log (dmesg)
eg:
[ 4302.798003] Start Seq = 00000048 [ 4306.938063] MtPsWatchDog(): HIT PsmPktCount/Dur: 0/1 on Wcid 2 (SW_PSM:[0|0])
[ 4306.938063]
[ 4306.938063]
[ 4306.938063]
[ 4306.938063]
[ 4369.804423] Rcv Wcid(2) AddBAReq
[ 4369.807715] Start Seq = 00000049
[ 4495.796112] Rcv Wcid(2) AddBAReq [ 4495.799568] Start Seq = 0000004b
[ 4505.794162] Rcv Wcid(2) AddBAReq
[ 4505.797454] Start Seq = 0000004c
[ 4571.804827] Rcv Wcid(2) AddBAReq
[ 4571.808229] Start Seq = 0000004d
[ 4639.795186] Rcv Wcid(2) AddBAReq
[ 4639.798501] Start Seq = 0000004e
[ 4705.798060] Rcv Wcid(2) AddBAReq
[ 4705.801362] Start Seq = 0000004f
[ 4734.558123] MtPsWatchDog(): HIT PsmPktCount/Dur: 0/1 on Wcid 1 (SW_PSM:[0|0])
[ 4734.558123]
[ 4734.558123]
[ 4734.558123]
[ 4734.558123] [ 4772.795176] Rcv Wcid(2) AddBAReq
[ 4772.798490] Start Seq = 00000050
[ 4840.790531] Rcv Wcid(2) AddBAReq
And repeat etc etc
Probably a simple fix and does not seem to cause any problems.
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