[ADTech]

Wildly fluctuating signal strength/quality swings is almost always one of the following:

1. Multi-path interference, usually moving trees.
2. Electrical or electronic interference, most commonly FM radio or power line nose, both on VHF channels.
3. Signal power at the edge of the "digital cliff".
4. Over amplification.

Different tuners have different capabilities in dealing with such signal impairments. Some handle it will well, others do not.

If you just added a splitter, then you may also need to consider either that the splitter is bad (swap ports) or the additional signal insertion loss of the splitter plus the coax leaves an inadequate amount of signal for the tuner.

Try swapping the TV sets and see if the issue stays with the set or if it stays with that drop location.