Netgear frequently has loss of all traffic (wifi and lan)

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Professionals assume responsibility for their mistakes whether it is due to a lack of product knowledge or not being thorough in their preperation to perform a task.   

That aside, check your signals.    Look for a low SNR ratio on the downstream channels or excessive power on the upload channels.   Out of spec values here can cause connection problems and if the modem misses enough timing signals it will reboot.   Check what firmware has been loaded on your device and check what configuration file has been pushed to the device.   Hopefully you have a record of what use to be on the device and can compare it to what is currently installed.     It sounds as if your modem is periodically rebooting which would explain the wifi outage.    Troubleshooting practices are to always ask 'what's changed to cause this new behaviour?' and since you have not replaced the device (you haven't right?), and you double checked that your cable is tight at the modem (you did right?),  and you did change service level..... well the first place you start looking is the last change(s) made and service level changes result in a new configuration file being pushed to the device.  It's possible that your device has started failing and it is just a coincidence that it correlated to the change in service, but we generally do not start with that assumption before eliminating other causes.    

Good luck!

O/k can see them now. The upstream power is  high and it may be intermittently fluctuating even higher to out of spec levels. That can cause random disconnects, spontaneous re-booting of the modem, speed, packet loss, and latency problems.

In a self troubleshooting effort to try to obtain better connectivity / more wiggle room, check to see if there are there any excess/unneeded coax cable splitters in the line leading to the modem that can be eliminated/re-configured. Any splitters that remain should be high quality and cable rated for 5-1002 MHz, bi-directional, and no gold colored garbage types like GE, RadioShack, RCA, Philips, Leviton, Magnavox, and Rocketfish from big box stores like Home Depot, Lowes, Target, Wal-Mart etc. Splitters should be swapped with known to be good / new ones to test

If there aren't any unneeded splitters that can be eliminated and if your coax wiring setup can't be reconfigured so that there is a single two way splitter connected directly off of the drop from the street/pole with one port feeding the modem and the other port feeding the rest of the house/equipment with additional splits as needed, and you've checked all the wiring and fittings for integrity and tightness and refresh them by taking them apart then check for and clean off any corrosion / oxidation on the center wire and put them back together again, then perhaps it's best to book a tech visit to investigate and correct.

Thank you for the replies!

I should have provided this information as well. This is in a new apartement building that was just built last year so the lines are new and there are no splitters. The connection is directly to the wall and that leads down to the demarcation point.

Something that seems to trigger these events (correlation isn't causation but...) lately is every time I open my Samsung SmartThings app (have a SmartThings hub v3 on the wifi network) on my s8 (also connected to the wifi via 5ghz) this happens. I was opening the app to turn on a lamp in my bedroom which is a zwave samsung smart bulb. I don't know how that could be but it has been a pattern. All day today no outages in the event log but I open my smartthings app and boom this shows up in the logs:

• 2020-2-24, 21:06:40 Critical (3) Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=14:59:c0:67:6d:70;CMTS-MAC=00:01:5c:74:64:57;CM-QOS=1.1;CM-VER=3.0;
• 2020-2-24, 21:02:20 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=14:59:c0:67:6d:70;CMTS-MAC=00:01:5c:74:64:57;CM-QOS=1.1;CM-VER=3.0;
• 2020-2-24, 21:02:20 Warning (5) MDD message timeout;CM-MAC=14:59:c0:67:6d:70;CMTS-MAC=00:01:5c:74:64:57;CM-QOS=1.1;CM-VER=3.0;

I noticed the downstream arrow on the netgear start flashing while the other lights were solid green.

What should the up and down stream channels be at for power and signal to noise?

SNR levels are defined in the troubleshooting guide here.  

One would hope using two devices on the 5 GHz band would not cause T3/T4 events on the modem.    I think your messages are coincidental.    See if you can force more failures by toggling the light a bunch of times.

MDU's (Multiple Dwelling Units) are particularly problematic for cable systems ! Perhaps it best to get a tech back out to investigate the demarc point, the coax cable drop from the pole, and the tap itself on the pole / pedestal. 

The high upstream power, the RF error log entries, and the downstream light on the modem all point to an intermittent RF signal impairment problem.

Here are the signal ranges from the troubleshooting tips sticky topic at the top of this board;

Downstream Power Levels: -8dBmV to  +10dBmV

Downstream Signal to Noise Ratio (SNR):  >35dB 

Upstream Power Level:  +25dBmV to +54dBmV

Upstream Signal to Noise Ratio (uSNR): >31dB  

Upstream Receive Power: -2dBmV to +2dBmV

The upstream power at 50 dB can easily fluctuate higher to being out of spec if there is a line / hardware problem.

Bear in mind that if the premises facing techs can not find or fix a problem at your residence / building, it is they who are responsible for escalating it to their line / network / maintenance dept. techs. The problem may lie beyond your building in the local neighborhood infrastructure somewhere but it is their S.O.P. to start at the home. Good luck with it ! Please post back with how things turn out.

P.S.: Bear in mind that anything on the LAN side / your home network / devices can NOT cause marginal signal levels, those RF error log entries, or the modem's downstream light to blink intermittently.