i've a lot of 3000L installed and https://speedtest.vet/ in all of this https://vidmate.bid/ the ethernet speed (with around 20mt of cat5E FTP) flapping from 1gbps to 100mbps then back fixed to 100mbps.
I've changed 3000L with a F300 and link is 1Gbps....
Any thinks is welcome..
All of ours are at 1gbit.
Link/speed flaps are almost always a cable issue.
Depending on your cable, grade of connector and the switch you are connecting to, link flaps and or speed flaps can happen.
The 3000L is a 10/100/1000 port with mdix and so far the ports seem to be very stable.
Your cable should be a minimum of utp cat5e outdoor rated, but stp, full foil is good. Make sure your cable has as few twists removed from the cable ends as possible. Its better to add half a twist rather than remove. Make sure you follow TIA-568 pinouts, it doesnt matter which of the two pinouts you use as long as it is the same on both ends. Always use pure copper network cables, CCA is cheap and readily available, pure copper is expensive but you get what you pay for. To determin if you have CCA in pure copper packaging, strip a single wire about an inch and scrape the surface with a hard carbon steel knife. Pure copper turns a bright redish color, CCA just gets shiney.
RJ-45 crimp on connectors are not all the same, there are differences for different cable types (solid vs stranded pairs) as well as different grades of connectors. You shouldnt need to pay high prices to get good ones, but also be aware that there are cheap ones that are not worth even looking at. Look for connectors that are either pass through type (better twist control) or made of good hard acrylic or both. You can tell by feel an acrylic one vs a cheap plastic one. Also look at the cable bite on the pins, these are insulation displacing and you should see 3 tips minimum inside where the wire is connected.
If you are using the Cambium supplied poe injector then the jumper cable from the supply to the switch should be of good quality premade. If you are not using the Cambium poe injector then switch to it for a bit to see if your main poe injector is at fault.
The switch you choose does not really matter, but using a higher quality switch will reduce issues. Also in some switches the ports are grouped with the magnetics, meaning you could have ports that are damaged or weak in a group. The Cisco switches we use are grouped in 4's, ports 1-4, 5-8, 9-12 etc. If port 5 goes dead, ports 6 - 8 can(but not always) show odd behavior such as link flaps). If you are using a good managed switch, check for crc errors. Crc errors are cable quality issues and are common with CCA cables.
We had 3 3000L's that wouldn't maintain gb even though the 1000Gps that they replaced worked just fine at Gb. In the end though replacing the ends fixed it and so far the 3000L's have not had further ethernet problems. It seems the 3000L's are a bit more likely to have ethernet problems than a 1000gps so make sure your cables/ends are perfect. In the case of towers were interference from RF is the problem you may need to take steps such as adding ferrite clamps, more/better shielding, better grounding to get a 3000L to work where a 1000 had no problems.
You can try disabling the Smart Speed feature. If this feautre is enabled device inhibits completion of the training phase, then after a few failed attempts, the device automatically adjusts the highest ability to the next lower speed: from 1000 to 100 to 10.